diff --git a/DESCRIPTION b/DESCRIPTION
index 59dccca..52e4bdc 100644
--- a/DESCRIPTION
+++ b/DESCRIPTION
@@ -1,6 +1,6 @@
 Package: broman
-Version: 0.83-1
-Date: 2024-05-07
+Version: 0.83-2
+Date: 2024-05-08
 Title: Karl Broman's R Code
 Description: Miscellaneous R functions, including functions related to
     graphics (mostly for base graphics), permutation tests, running
diff --git a/NEWS.md b/NEWS.md
index 149fb57..fa7588f 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -1,12 +1,12 @@
 Revision history for the R/broman package
 -----------------------------------------
 
-## Version 0.83, 2024-05-07
+## Version 0.83-2, 2024-05-08
 
 - Allow `NA`s in `runningmean()` and `runningratio()`.
 
 - Add `scale` argument to `time_axis()` to allow control over time
-  labels it gives.
+  labels it gives, and `format` argument for customized labels.
 
 
 ## Version 0.82, 2024-05-05
diff --git a/R/time_axis.R b/R/time_axis.R
index b760186..3181693 100644
--- a/R/time_axis.R
+++ b/R/time_axis.R
@@ -10,6 +10,8 @@
 #'    `"sec"`, `"min"`, `"hr"`, or `"day"`. If NULL, scale is chosen
 #'    based on the `times`.
 #'
+#' @param format If provided, used in place of `scale` for formating the times.
+
 #' @return A data frame with the numeric values to plot plus labels to use.
 #'
 #' @export
@@ -30,15 +32,19 @@
 #' grayplot(x, y, xat=NA, vlines=xax$x)
 #' axis(side=1, at=xax$x, labels=xax$label, mgp=c(2.1, 0.5, 0), tick=FALSE)
 #'
-#'
 #' # labels as seconds
 #' x <- seq(as.POSIXct("2024-05-01 11:23:05.3"), as.POSIXct("2024-05-01 11:23:55.7"), length.out=n)
 #' xax <- time_axis(x)
 #' grayplot(x, y, xat=NA, vlines=xax$x)
 #' axis(side=1, at=xax$x, labels=xax$label, mgp=c(2.1, 0.5, 0), tick=FALSE)
+#'
+#' # custom time format
+#' xax <- time_axis(x, format="%H:%M:%S")
+#' grayplot(x, y, xat=NA, vlines=xax$x)
+#' axis(side=1, at=xax$x, labels=xax$label, mgp=c(2.1, 0.5, 0), tick=FALSE)
 
 time_axis <-
-    function(times, n=8, scale=NULL)
+    function(times, n=8, scale=NULL, format=NULL)
 {
     if(!("POSIXct" %in% class(times) || "POSIXt" %in% class(times))) {
         stop("times should be a vector of date/times")
@@ -46,6 +52,11 @@ time_axis <-
 
     prettyx <- pretty(times, n=n)
 
+    if(!is.null(format)) { # use custom format, ignoring scale
+        return(data.frame(x=prettyx,
+                          labels=format(prettyx, format)))
+    }
+
     r <- range(as.numeric(times))
     dr <- diff(r)
     # determine range
diff --git a/man/time_axis.Rd b/man/time_axis.Rd
index a120b18..2f7ff0a 100644
--- a/man/time_axis.Rd
+++ b/man/time_axis.Rd
@@ -4,7 +4,7 @@
 \alias{time_axis}
 \title{Set up a time-based axis}
 \usage{
-time_axis(times, n = 8, scale = NULL)
+time_axis(times, n = 8, scale = NULL, format = NULL)
 }
 \arguments{
 \item{times}{A vector of date/times that will be plotted}
@@ -14,6 +14,8 @@ time_axis(times, n = 8, scale = NULL)
 \item{scale}{Forced choice of scale for axis labels:
 \code{"sec"}, \code{"min"}, \code{"hr"}, or \code{"day"}. If NULL, scale is chosen
 based on the \code{times}.}
+
+\item{format}{If provided, used in place of \code{scale} for formating the times.}
 }
 \value{
 A data frame with the numeric values to plot plus labels to use.
@@ -37,10 +39,14 @@ xax <- time_axis(x)
 grayplot(x, y, xat=NA, vlines=xax$x)
 axis(side=1, at=xax$x, labels=xax$label, mgp=c(2.1, 0.5, 0), tick=FALSE)
 
-
 # labels as seconds
 x <- seq(as.POSIXct("2024-05-01 11:23:05.3"), as.POSIXct("2024-05-01 11:23:55.7"), length.out=n)
 xax <- time_axis(x)
 grayplot(x, y, xat=NA, vlines=xax$x)
 axis(side=1, at=xax$x, labels=xax$label, mgp=c(2.1, 0.5, 0), tick=FALSE)
+
+# custom time format
+xax <- time_axis(x, format="\%H:\%M:\%S")
+grayplot(x, y, xat=NA, vlines=xax$x)
+axis(side=1, at=xax$x, labels=xax$label, mgp=c(2.1, 0.5, 0), tick=FALSE)
 }