Cannot understand this measure I inherited

[kkirner]

Hi, I inherited this measure from someone who was building reports for our company before I started.  When used as a filter it seems to limit the data returned to revenue items for the current month or the previous month.   Would anyone be kind enough to try to interpret it for me?

MonthOnlyLedger =

VAR monthNum = IF(MONTH(TODAY()) = 1, 12, MONTH(TODAY())-1)

VAR yearNum = YEAR(TODAY()-31)

VAR zeroNum = INT(CONCATENATE(0, monthNum))

Return

OR(CONTAINSSTRING(SPSRevenue[DisbursedToLedger], IF(monthNum > 9, CONCATENATE(RIGHT(yearNum,2), monthNum), CONCATENATE(RIGHT(yearNum,2), CONCATENATE("0", monthNum)))), CONTAINSSTRING(SPSRevenue[DisbursedToLedger], FORMAT(TODAY(), "yymm")))

[kkirner]

@tamerj1 Thank you very much.  I really appreciate the explanation of each variable and the simpler revision.

[tamerj1 · Accepted solution]

@kkirner 
Yes yoy are right. It restricts the calculation for the last two months.

MonthOnlyLedger =
VAR monthNum =
    IF ( MONTH ( TODAY () ) = 1, 12, MONTH ( TODAY () ) - 1 ) --Retrieves the previous Month Number
VAR yearNum =
    YEAR ( TODAY () - 31 ) -- Retrieves the year of the previous month
VAR zeroNum =
    INT ( CONCATENATE ( 0, monthNum ) ) -- This does absolutely nothing. It just returns monthNum and it is not used further in the code.
RETURN
    OR (
        CONTAINSSTRING (
            SPSRevenue[DisbursedToLedger],
            -- This column has the folrmat "YYMM"
            IF (
                monthNum > 9,
                CONCATENATE ( RIGHT ( yearNum, 2 ), monthNum ),
                CONCATENATE ( RIGHT ( yearNum, 2 ), CONCATENATE ( "0", monthNum ) ) --The IF statement is just to tackle the month forrmat (one or two digits)
            )
        ),
        CONTAINSSTRING ( SPSRevenue[DisbursedToLedger], FORMAT ( TODAY (), "yymm" ) )
    )
-- the above means if in this month or previous month return true else false

Can be simplified as

MonthOnlyLedger =
VAR ThisYearMonth =
    FORMAT ( TODAY (), "YYMM" )
VAR PreviousYearMonth =
    FORMAT ( EOMONTH ( TODAY (), -1 ), "YYMM" )
RETURN
    OR (
        CONTAINSSTRING ( SPSRevenue[DisbursedToLedger], ThisYearMonth ),
        CONTAINSSTRING ( SPSRevenue[DisbursedToLedger], PreviousYearMonth )
    )