diff --git a/R/archive.R b/R/archive.R
index 2f6af5e0..61eca1af 100644
--- a/R/archive.R
+++ b/R/archive.R
@@ -584,7 +584,7 @@ epi_archive =
 #'   details. 
 #' @importFrom data.table key
 #' @importFrom rlang !! !!! enquo quo_is_missing enquos is_quosure sym syms
-          slide = function(f, ..., n, group_by, ref_time_values, 
+          slide = function(f, ..., before, group_by, ref_time_values, 
                            time_step, new_col_name = "slide_value",
                            as_list_col = FALSE, names_sep = "_",
                            all_rows = FALSE) { 
@@ -597,10 +597,22 @@ epi_archive =
               ref_time_values = ref_time_values[ref_time_values %in%
                                                 unique(self$DT$time_value)]
             }
-              
+
+            # Validate and pre-process `before`:
+            if (missing(before)) {
+              Abort("`before` is required (and must be passed by name);
+                     if you did not want to apply a sliding window but rather
+                     to map `as_of` and `f` across various `ref_time_values`,
+                     pass a large `before` value (e.g., if time steps are days,
+                     `before=365000`).")
+            }
+            before <- vctrs::vec_cast(before, integer())
+            if (length(before) != 1L || is.na(before) || before < 0L) {
+              Abort("`before` must be length-1, non-NA, non-negative")
+            }
+
             # If a custom time step is specified, then redefine units 
-            before_num = n-1
-            if (!missing(time_step)) before_num = time_step(n-1)
+            if (!missing(time_step)) before <- time_step(before)
             
             # What to group by? If missing, set according to internal keys;
             # otherwise, tidyselect.
@@ -673,12 +685,13 @@ epi_archive =
             if (!missing(f)) {
               if (rlang::is_formula(f)) f = rlang::as_function(f)
               
-              x = purrr::map_dfr(ref_time_values, function(t) {
-                self$as_of(t, min_time_value = t - before_num) %>%
+              x = purrr::map_dfr(ref_time_values, function(ref_time_value) {
+                self$as_of(ref_time_value,
+                           min_time_value = ref_time_value - before) %>%
                   dplyr::group_by(!!!group_by) %>%
                   dplyr::group_modify(comp_one_grp,
                                       f = f, ..., 
-                                      time_value = t,
+                                      time_value = ref_time_value,
                                       key_vars = key_vars,
                                       new_col = new_col,
                                       .keep = TRUE) %>%
@@ -700,12 +713,13 @@ epi_archive =
               f = function(x, quo, ...) rlang::eval_tidy(quo, x)
               new_col = sym(names(rlang::quos_auto_name(quos)))
 
-              x = purrr::map_dfr(ref_time_values, function(t) {
-                self$as_of(t, min_time_value = t - before_num) %>%
+              x = purrr::map_dfr(ref_time_values, function(ref_time_value) {
+                self$as_of(ref_time_value,
+                           min_time_value = ref_time_value - before) %>%
                   dplyr::group_by(!!!group_by) %>%
                   dplyr::group_modify(comp_one_grp,
                                       f = f, quo = quo,
-                                      time_value = t,
+                                      time_value = ref_time_value,
                                       key_vars = key_vars,
                                       new_col = new_col,
                                       .keep = TRUE) %>%
diff --git a/R/methods-epi_archive.R b/R/methods-epi_archive.R
index 3387c935..6cffa144 100644
--- a/R/methods-epi_archive.R
+++ b/R/methods-epi_archive.R
@@ -358,10 +358,21 @@ epix_merge = function(x, y,
 #' @param ... Additional arguments to pass to the function or formula specified
 #'   via `f`. Alternatively, if `f` is missing, then the current argument is
 #'   interpreted as an expression for tidy evaluation.
-#' @param n Number of time steps to use in the running window. For example, if
-#'   `n = 7`, and one time step is one day, then to produce a value on January 7
-#'   we apply the given function or formula to data in between January 1 and
-#'   7.
+#' @param before How far `before` each `ref_time_value` should the sliding
+#'   window extend? If provided, should be a single, non-NA,
+#'   [integer-compatible][vctrs::vec_cast] number of time steps. This window
+#'   endpoint is inclusive. For example, if `before = 7`, and one time step is
+#'   one day, then to produce a value for a `ref_time_value` of January 8, we
+#'   apply the given function or formula to data (for each group present) with
+#'   `time_value`s from January 1 onward, as they were reported on January 8.
+#'   For typical disease surveillance sources, this will not include any data
+#'   with a `time_value` of January 8, and, depending on the amount of reporting
+#'   latency, may not include January 7 or even earlier `time_value`s. (If
+#'   instead the archive were to hold nowcasts instead of regular surveillance
+#'   data, then we would indeed expect data for `time_value` January 8. If it
+#'   were to hold forecasts, then we would expect data for `time_value`s after
+#'   January 8, and the sliding window would extend as far after each
+#'   `ref_time_value` as needed to include all such `time_value`s.)
 #' @param group_by The variable(s) to group by before slide computation. If
 #'   missing, then the keys in the underlying data table, excluding `time_value`
 #'   and `version`, will be used for grouping. To omit a grouping entirely, use
@@ -396,10 +407,14 @@ epix_merge = function(x, y,
 #'   values.
 #'
 #' @details Two key distinctions between inputs to the current function and
-#'   `epi_slide()`:
-#'   1. `epix_slide()` uses windows that are **always right-aligned** (in
-#'   `epi_slide()`, custom alignments could be specified using the `align` or
-#'   `before` arguments).
+#'   [`epi_slide()`]:
+#'   1. `epix_slide()` doesn't accept an `after` argument; its windows extend
+#'   from `before` time steps before a given `ref_time_value` through the last
+#'   `time_value` available as of version `ref_time_value` (typically, this
+#'   won't include `ref_time_value` itself, as observations about a particular
+#'   time interval (e.g., day) are only published after that time interval ends);
+#'   `epi_slide` windows extend from `before` time steps before a
+#'   `ref_time_value` through `after` time steps after `ref_time_value`.
 #'   2. `epix_slide()` uses a `group_by` to specify the grouping upfront (in
 #'   `epi_slide()`, this would be accomplished by a preceding function call to
 #'   `dplyr::group_by()`).
@@ -422,11 +437,11 @@ epix_merge = function(x, y,
 #' Finally, this is simply a wrapper around the `slide()` method of the
 #'   `epi_archive` class, so if `x` is an `epi_archive` object, then:
 #'   ```
-#'   epix_slide(x, new_var = comp(old_var), n = 120)
+#'   epix_slide(x, new_var = comp(old_var), before = 119)
 #'   ```
 #'   is equivalent to:
 #'   ```
-#'   x$slide(x, new_var = comp(old_var), n = 120)
+#'   x$slide(new_var = comp(old_var), before = 119)
 #'   ```
 #'
 #' @importFrom rlang enquo
@@ -444,15 +459,15 @@ epix_merge = function(x, y,
 #'                       by = "1 day")
 #' epix_slide(x = archive_cases_dv_subset,
 #'            f = ~ mean(.x$case_rate_7d_av),
-#'            n = 3,
+#'            before = 2,
 #'            group_by = geo_value,
 #'            ref_time_values = time_values,
 #'            new_col_name = 'case_rate_3d_av')
-epix_slide = function(x, f, ..., n, group_by, ref_time_values,
+epix_slide = function(x, f, ..., before, group_by, ref_time_values,
                       time_step, new_col_name = "slide_value",
                       as_list_col = FALSE, names_sep = "_", all_rows = FALSE) {
   if (!inherits(x, "epi_archive")) Abort("`x` must be of class `epi_archive`.")
-  return(x$slide(f, ..., n = n,
+  return(x$slide(f, ..., before = before,
                  group_by = {{group_by}},
                  ref_time_values = ref_time_values,
                  time_step = time_step,
diff --git a/man/epi_archive.Rd b/man/epi_archive.Rd
index 026f27e1..998ade9e 100644
--- a/man/epi_archive.Rd
+++ b/man/epi_archive.Rd
@@ -277,7 +277,7 @@ details.
 \if{html}{\out{<div class="r">}}\preformatted{epi_archive$slide(
   f,
   ...,
-  n,
+  before,
   group_by,
   ref_time_values,
   time_step,
diff --git a/man/epix_slide.Rd b/man/epix_slide.Rd
index 79e9c1c3..bbeb51d4 100644
--- a/man/epix_slide.Rd
+++ b/man/epix_slide.Rd
@@ -8,7 +8,7 @@ epix_slide(
   x,
   f,
   ...,
-  n,
+  before,
   group_by,
   ref_time_values,
   time_step,
@@ -34,10 +34,21 @@ sliding window of \code{n} time steps.}
 via \code{f}. Alternatively, if \code{f} is missing, then the current argument is
 interpreted as an expression for tidy evaluation.}
 
-\item{n}{Number of time steps to use in the running window. For example, if
-\code{n = 7}, and one time step is one day, then to produce a value on January 7
-we apply the given function or formula to data in between January 1 and
-7.}
+\item{before}{How far \code{before} each \code{ref_time_value} should the sliding
+window extend? If provided, should be a single, non-NA,
+\link[vctrs:vec_cast]{integer-compatible} number of time steps. This window
+endpoint is inclusive. For example, if \code{before = 7}, and one time step is
+one day, then to produce a value for a \code{ref_time_value} of January 8, we
+apply the given function or formula to data (for each group present) with
+\code{time_value}s from January 1 onward, as they were reported on January 8.
+For typical disease surveillance sources, this will not include any data
+with a \code{time_value} of January 8, and, depending on the amount of reporting
+latency, may not include January 7 or even earlier \code{time_value}s. (If
+instead the archive were to hold nowcasts instead of regular surveillance
+data, then we would indeed expect data for \code{time_value} January 8. If it
+were to hold forecasts, then we would expect data for \code{time_value}s after
+January 8, and the sliding window would extend as far after each
+\code{ref_time_value} as needed to include all such \code{time_value}s.)}
 
 \item{group_by}{The variable(s) to group by before slide computation. If
 missing, then the keys in the underlying data table, excluding \code{time_value}
@@ -89,11 +100,15 @@ examples.
 }
 \details{
 Two key distinctions between inputs to the current function and
-\code{epi_slide()}:
+\code{\link[=epi_slide]{epi_slide()}}:
 \enumerate{
-\item \code{epix_slide()} uses windows that are \strong{always right-aligned} (in
-\code{epi_slide()}, custom alignments could be specified using the \code{align} or
-\code{before} arguments).
+\item \code{epix_slide()} doesn't accept an \code{after} argument; its windows extend
+from \code{before} time steps before a given \code{ref_time_value} through the last
+\code{time_value} available as of version \code{ref_time_value} (typically, this
+won't include \code{ref_time_value} itself, as observations about a particular
+time interval (e.g., day) are only published after that time interval ends);
+\code{epi_slide} windows extend from \code{before} time steps before a
+\code{ref_time_value} through \code{after} time steps after \code{ref_time_value}.
 \item \code{epix_slide()} uses a \code{group_by} to specify the grouping upfront (in
 \code{epi_slide()}, this would be accomplished by a preceding function call to
 \code{dplyr::group_by()}).
@@ -117,12 +132,12 @@ version-aware sliding is necessary (as it its purpose).
 Finally, this is simply a wrapper around the \code{slide()} method of the
 \code{epi_archive} class, so if \code{x} is an \code{epi_archive} object, then:
 
-\if{html}{\out{<div class="sourceCode">}}\preformatted{epix_slide(x, new_var = comp(old_var), n = 120)
+\if{html}{\out{<div class="sourceCode">}}\preformatted{epix_slide(x, new_var = comp(old_var), before = 119)
 }\if{html}{\out{</div>}}
 
 is equivalent to:
 
-\if{html}{\out{<div class="sourceCode">}}\preformatted{x$slide(x, new_var = comp(old_var), n = 120)
+\if{html}{\out{<div class="sourceCode">}}\preformatted{x$slide(new_var = comp(old_var), before = 119)
 }\if{html}{\out{</div>}}
 }
 \examples{
@@ -138,7 +153,7 @@ time_values <- seq(as.Date("2020-06-01"),
                       by = "1 day")
 epix_slide(x = archive_cases_dv_subset,
            f = ~ mean(.x$case_rate_7d_av),
-           n = 3,
+           before = 2,
            group_by = geo_value,
            ref_time_values = time_values,
            new_col_name = 'case_rate_3d_av')
diff --git a/tests/testthat/test-epix_fill_through_version.R b/tests/testthat/test-epix_fill_through_version.R
index 03e9c504..1d78bf49 100644
--- a/tests/testthat/test-epix_fill_through_version.R
+++ b/tests/testthat/test-epix_fill_through_version.R
@@ -11,9 +11,10 @@ test_that("epix_fill_through_version mirrors input when it is sufficiently up to
   # edition 3, which is based on `waldo::compare` rather than `base::identical`;
   # `waldo::compare` in waldo >=0.3.1 appears (as of 0.4.0) to compare R6
   # objects by contents rather than address (in a way that is tested but maybe
-  # not guaranteed via user docs). Use `local_edition` to ensure we use edition
-  # 3 here.
-  local_edition(3)
+  # not guaranteed via user docs). Use `testthat::local_edition` to ensure we
+  # use testthat edition 3 here (use `testthat::` to prevent ambiguity with
+  # `readr`).
+  testthat::local_edition(3)
   expect_identical(ea_orig, ea_trivial_fill_na1)
   expect_identical(ea_orig, ea_trivial_fill_na2)
   expect_identical(ea_orig, ea_trivial_fill_locf)
@@ -30,9 +31,9 @@ test_that("epix_fill_through_version can extend observed versions, gives expecte
   ea_fill_na = epix_fill_through_version(ea_orig, later_unobserved_version, "na")
   ea_fill_locf = epix_fill_through_version(ea_orig, later_unobserved_version, "locf")
 
-  # We use edition 3 features here, passing `ignore_attr` to `waldo::compare`.
-  # Ensure we are using edition 3:
-  local_edition(3)
+  # We use testthat edition 3 features here, passing `ignore_attr` to
+  # `waldo::compare`. Ensure we are using edition 3:
+  testthat::local_edition(3)
   withCallingHandlers({
     expect_identical(ea_fill_na$versions_end, later_unobserved_version)
     expect_identical(tibble::as_tibble(ea_fill_na$as_of(first_unobserved_version)),
diff --git a/tests/testthat/test-epix_merge.R b/tests/testthat/test-epix_merge.R
index 51f2c3c6..8a873926 100644
--- a/tests/testthat/test-epix_merge.R
+++ b/tests/testthat/test-epix_merge.R
@@ -58,7 +58,7 @@ test_that("epix_merge merges and carries forward updates properly", {
   )
   # We rely on testthat edition 3 expect_identical using waldo, not identical. See
   # test-epix_fill_through_version.R comments for details.
-  local_edition(3)
+  testthat::local_edition(3)
   expect_identical(xy, xy_expected)
 })
 
diff --git a/tests/testthat/test-epix_slide.R b/tests/testthat/test-epix_slide.R
new file mode 100644
index 00000000..9a11c64a
--- /dev/null
+++ b/tests/testthat/test-epix_slide.R
@@ -0,0 +1,65 @@
+library(dplyr)
+
+test_that("epix_slide only works on an epi_archive",{
+  expect_error(epix_slide(data.frame(x=1)))
+})
+
+x <- tibble::tribble(~version, ~time_value, ~binary,
+                     4,       c(1:3),       2^(1:3),
+                     5,       c(1:2,4),     2^(4:6),
+                     6,       c(1:2,4:5),   2^(7:10),
+                     7,       2:6,          2^(11:15)) %>%
+  tidyr::unnest(c(time_value,binary))
+
+xx <- bind_cols(geo_value = rep("x",15), x) %>%
+  as_epi_archive()
+
+test_that("epix_slide works as intended",{
+  xx1 <- epix_slide(x = xx,
+                    f = ~ sum(.x$binary),
+                    before = 2,
+                    group_by = geo_value,
+                    new_col_name = "sum_binary")
+  
+  xx2 <- tibble(geo_value = rep("x",3),
+                # 7 should also be there below; this is a bug on issue #153
+                time_value = c(4,5,6),
+                sum_binary = c(2^3+2^2,
+                               2^6+2^3,
+                               2^10+2^9)) %>%
+    as_epi_df(as_of = 1) # Also a bug (issue #213)
+  
+  expect_identical(xx1,xx2) # *
+  
+  xx3 <- xx$slide(f = ~ sum(.x$binary),
+                  before = 2,
+                  group_by = "geo_value",
+                  new_col_name = 'sum_binary')
+  
+  expect_identical(xx1,xx3) # This and * Imply xx2 and xx3 are identical
+})
+
+test_that("epix_slide `before` validation works", {
+  expect_error(xx$slide(f = ~ sum(.x$binary)),
+               "`before` is required")
+  expect_error(xx$slide(f = ~ sum(.x$binary), before=NA),
+               "`before`.*NA")
+  expect_error(xx$slide(f = ~ sum(.x$binary), before=-1),
+               "`before`.*negative")
+  expect_error(xx$slide(f = ~ sum(.x$binary), before=1.5),
+               regexp="before",
+               class="vctrs_error_incompatible_type")
+  # We might want to allow this at some point (issue #219):
+  expect_error(xx$slide(f = ~ sum(.x$binary), before=Inf),
+               regexp="before",
+               class="vctrs_error_incompatible_type")
+  # (wrapper shouldn't introduce a value:)
+  expect_error(epix_slide(xx, f = ~ sum(.x$binary)), "`before` is required")
+  # These `before` values should be accepted:
+  expect_error(xx$slide(f = ~ sum(.x$binary), before=0),
+               NA)
+  expect_error(xx$slide(f = ~ sum(.x$binary), before=2L),
+               NA)
+  expect_error(xx$slide(f = ~ sum(.x$binary), before=365000),
+               NA)
+})
diff --git a/tests/testthat/test-methods-epi_archive.R b/tests/testthat/test-methods-epi_archive.R
index d0434f59..02630595 100644
--- a/tests/testthat/test-methods-epi_archive.R
+++ b/tests/testthat/test-methods-epi_archive.R
@@ -71,13 +71,13 @@ test_that("quosure passing issue in epix_slide is resolved + other potential iss
                       compactify = TRUE)
   reference_by_modulus = epix_slide(x = ea,
                                       f = ~ mean(.x$case_rate_7d_av),
-                                      n = 3,
+                                      before = 2,
                                       group_by = modulus,
                                       ref_time_values = time_values,
                                       new_col_name = 'case_rate_3d_av')
   reference_by_both = epix_slide(x = ea,
                                  f = ~ mean(.x$case_rate_7d_av),
-                                 n = 3,
+                                 before = 2,
                                  group_by = c(geo_value, modulus),
                                  ref_time_values = time_values,
                                  new_col_name = 'case_rate_3d_av')
@@ -85,7 +85,7 @@ test_that("quosure passing issue in epix_slide is resolved + other potential iss
   expect_identical(
     ea$slide(
       f = ~ mean(.x$case_rate_7d_av),
-      n = 3,
+      before = 2,
       group_by = modulus,
       ref_time_values = time_values,
       new_col_name = 'case_rate_3d_av'
@@ -96,7 +96,7 @@ test_that("quosure passing issue in epix_slide is resolved + other potential iss
   expect_identical(
     epix_slide(x = ea,
                f = ~ mean(.x$case_rate_7d_av),
-               n = 3,
+               before = 2,
                group_by = "modulus",
                ref_time_values = time_values,
                new_col_name = 'case_rate_3d_av'),
@@ -105,7 +105,7 @@ test_that("quosure passing issue in epix_slide is resolved + other potential iss
   expect_identical(
     ea$slide(
       f = ~ mean(.x$case_rate_7d_av),
-      n = 3,
+      before = 2,
       group_by = "modulus",
       ref_time_values = time_values,
       new_col_name = 'case_rate_3d_av'
@@ -121,7 +121,7 @@ test_that("quosure passing issue in epix_slide is resolved + other potential iss
   expect_identical(
     epix_slide(x = ea,
                f = ~ mean(.x$case_rate_7d_av),
-               n = 3,
+               before = 2,
                group_by = tidyselect::all_of(my_group_by),
                ref_time_values = time_values,
                new_col_name = 'case_rate_3d_av'),
@@ -130,7 +130,7 @@ test_that("quosure passing issue in epix_slide is resolved + other potential iss
   expect_identical(
     ea$slide(
       f = ~ mean(.x$case_rate_7d_av),
-      n = 3,
+      before = 2,
       group_by = tidyselect::all_of(my_group_by),
       ref_time_values = time_values,
       new_col_name = 'case_rate_3d_av'
@@ -141,7 +141,7 @@ test_that("quosure passing issue in epix_slide is resolved + other potential iss
   expect_identical(
     epix_slide(x = ea,
                f = ~ mean(.x$case_rate_7d_av),
-               n = 3,
+               before = 2,
                ref_time_values = time_values,
                new_col_name = 'case_rate_3d_av'),
     reference_by_both
@@ -149,7 +149,7 @@ test_that("quosure passing issue in epix_slide is resolved + other potential iss
   expect_identical(
     ea$slide(
       f = ~ mean(.x$case_rate_7d_av),
-      n = 3,
+      before = 2,
       ref_time_values = time_values,
       new_col_name = 'case_rate_3d_av'
     ),
diff --git a/vignettes/advanced.Rmd b/vignettes/advanced.Rmd
index 5514eaaa..8b2eb16f 100644
--- a/vignettes/advanced.Rmd
+++ b/vignettes/advanced.Rmd
@@ -61,12 +61,12 @@ df %>%
 df %>% 
   mutate(version = time_value) %>% 
   as_epi_archive() %>%
-  epix_slide(x_2dav = mean(x), n = 2, ref_time_values = as.Date("2020-06-02"))
+  epix_slide(x_2dav = mean(x), before = 1, ref_time_values = as.Date("2020-06-02"))
 
 df %>% 
   mutate(version = time_value) %>% 
   as_epi_archive() %>%
-  epix_slide(~ mean(.x$x), n = 2, ref_time_values = as.Date("2020-06-02"))
+  epix_slide(~ mean(.x$x), before = 1, ref_time_values = as.Date("2020-06-02"))
 ```
 
 When the slide computation returns an atomic vector (rather than a single value)
@@ -153,7 +153,7 @@ df %>%
   as_epi_archive() %>%
   epix_slide(a = data.frame(x_2dav = mean(x), x_2dma = mad(x)),
              ref_time_values = as.Date("2020-06-02"),
-             n = 2, as_list_col = FALSE, names_sep = NULL)
+             before = 1, as_list_col = FALSE, names_sep = NULL)
 ```
 
 ## Multi-row outputs
@@ -354,7 +354,7 @@ k_week_ahead <- function(x, ahead = 7, as_of = TRUE) {
     x %>%
       epix_slide(fc = prob_arx(percent_cli, case_rate_7d_av, geo_value, time_value, 
                                args = prob_arx_args(ahead = ahead)), 
-                 n = 120, ref_time_values = fc_time_values) %>%
+                 before = 119, ref_time_values = fc_time_values) %>%
       mutate(target_date = time_value + ahead, as_of = TRUE, 
              geo_value = fc_geo_value)
   }
diff --git a/vignettes/archive.Rmd b/vignettes/archive.Rmd
index b78644ad..588b0c88 100644
--- a/vignettes/archive.Rmd
+++ b/vignettes/archive.Rmd
@@ -357,8 +357,9 @@ fc_time_values <- seq(as.Date("2020-08-01"),
                       as.Date("2021-12-01"), 
                       by = "1 month")
 
-z <- epix_slide(x, fc = prob_arx(x = percent_cli, y = case_rate_7d_av), n = 120, 
-                ref_time_values = fc_time_values, group_by = geo_value)
+z <- epix_slide(x, fc = prob_arx(x = percent_cli, y = case_rate_7d_av),
+                before  = 119, ref_time_values = fc_time_values,
+                group_by = geo_value)
 
 head(z, 10)
 ```
@@ -387,7 +388,7 @@ x_latest <- epix_as_of(x, max_version = max(x$DT$version))
 k_week_ahead <- function(x, ahead = 7, as_of = TRUE) {
   if (as_of) {
     x %>%
-      epix_slide(fc = prob_arx(percent_cli, case_rate_7d_av, ahead = ahead), n = 120,
+      epix_slide(fc = prob_arx(percent_cli, case_rate_7d_av, ahead = ahead), before = 119,
                  ref_time_values = fc_time_values, group_by = geo_value) %>%
       mutate(target_date = time_value + ahead, as_of = TRUE) 
   }
diff --git a/vignettes/compactify.Rmd b/vignettes/compactify.Rmd
index 034235b3..ecb227ca 100644
--- a/vignettes/compactify.Rmd
+++ b/vignettes/compactify.Rmd
@@ -102,7 +102,7 @@ speeds <- rbind(speeds, speed_test(iterate_as_of,"as_of_1000x"))
 
 # Performance of slide
 slide_median <- function(my_ea) {
-    my_ea$slide(median = median(case_rate_7d_av), n = 7)
+    my_ea$slide(median = median(case_rate_7d_av), before = 7)
 }
 
 speeds <- rbind(speeds, speed_test(slide_median,"slide_median"))