Grant and Hill reveal that the Gregorian calendar months are not scientific division of time.
“The calendar month is an arbitrary division of time, and the number of days varies from 28 to 31. ---------Thirty days has September,
April, June, and November,
All the rest have thirty one,
Excepting February alone,
This has but twenty- eight days clear;
and twenty-nine in each Leap- year.” Grant and Hill (1965:42)