diff --git a/datetimes.qmd b/datetimes.qmd
index 33bbe1e..f272f11 100644
--- a/datetimes.qmd
+++ b/datetimes.qmd
@@ -409,7 +409,10 @@ dyears(1)
 ```
 
 Durations always record the time span in seconds.
-Larger units are created by converting minutes, hours, days, weeks, and years to seconds at the standard rate (60 seconds in a minute, 60 minutes in an hour, 24 hours in day, 7 days in a week, 365 days in a year).
+Larger units are created by converting minutes, hours, days, weeks, and years to seconds: 60 seconds in a minute, 60 minutes in an hour, 24 hours in a day, and 7 days in a week.
+Larger time units are more problematic.
+A year is uses the "average" number of days in a year, i.e. 365.25.
+There's no way to convert a month to a duration, because there's just too much variation.
 
 You can add and multiply durations: