diff --git a/API.txt b/API.txt
index 892508e..1475bb7 100644
--- a/API.txt
+++ b/API.txt
@@ -375,8 +375,8 @@ graphs. If "fillColor" is null (default), the color for the data
 series is used.
 
 Note that the options that take numbers works in units of pixels, but
-"barWidth" is the width of the bars in units of the x axis to allow
-for scaling.
+"barWidth" is the width of the bars in units of the x axis (e.g. for
+time series it's in milliseconds).
 
 The "colors" array specifies a default color theme to get colors for
 the data series from. You can specify as many colors as you like, like