It's based on the settings (10, 30, 60, 30).
Originaly settings are (9, 26, 52, 26) based on this statement :
"As a result, the number nine represents a week and a half of trading; 26 equals the number of trading days in a typical month (30 minus four Sundays); and 52 equals two months of trading days."
For bitcoin the market is open 7 days a week every month.
- 1st number : 7+3.5 = 10 (better because of low on sunday)
- 2nd and 4th numbers : 30 days in a month
- 3rd number : number of days in 2 month : 2*30 = 60 days
I am open to any kind of suggestion.