Deriving 0CALMONTH from other time characteristics

Hi,

I have a <b>datasource</b> that delivers <b>0CALWEEK, OCALQUARTER and 0FISCPER</b> as time characteristics.

I have an <b>Infocube</b> that <b>also</b> contains <b>0CALMONTH</b> as as an additional Time Characteristic.

Is there a <b>way to derive 0CALMONTH from these other time characteristics in the update rules?</b>

Thanks a lot

Christian