Campbell Scientific CR800 and CR850 Measurement and Control Systems - Manual (Page 218)

Section 7. Installation
218
'If it is a leap year, use this section.
If (LeapYear = True) Then
Select Case DOY
Case Is < 32
Month = 1
Date = DOY
Case Is < 61
Month = 2
Date = DOY + -31
Case Is < 92
Month = 3
Date = DOY + -60
Case Is < 122
Month = 4
Date = DOY + -91
Case Is < 153
Month = 5
Date = DOY + -121
Case Is < 183
Month = 6
Date = DOY + -152
Case Is < 214
Month = 7
Date = DOY + -182
Case Is < 245
Month = 8
Date = DOY + -213
Case Is < 275
Month = 9
Date = DOY + -244
Case Is < 306
Month = 10
Date = DOY + -274
Case Is < 336
Month = 11
Date = DOY + -305
Case Is < 367
Month = 12
Date = DOY + -335
EndSelect
'If it is not a leap year, use this section.
Else
Select Case DOY
Case Is < 32
Month = 1
Date = DOY
Case Is < 60
Month = 2
Date = DOY + -31
Case Is < 91
Month = 3
Date = DOY + -59