I am using the corner label feature in Arcmap 10. This allows you to set the "Numer of principal digits" and the "Number of base digits". What do these properties refer to?
I just tried Corner Labels for the first time and can see how you can use Principal and Base digits to change how many digits are full script and super script.
I used PCS MGA Zone 54 on the data frame for some Australian test data stored in GCS GDA94 and it seemed like changing the Principal digits overrode changing the Base ones (but only tested quickly).
I used http://mappingcenter.esri.com/index.cfm?fa=ask.answers&q=1301 to help me get into them, and there's a bit of help in http://www.fgdc.gov/usng/resources/esriadding-grids-and-graticules.pdf too.
I could not locate anything specific in the Online Help to describe what Principal and Base digits are.