How to check the greatest revision no in the expression and to get the data for the greatest rev no

[#1]

i have written the expression to get the sum of plan qty for a month and showing as target in the bar graph but the thing is in a month many revisions will happen for a plan so i need to pick up th greatest revision and i ahve to sum up the gratest revision plan qty and have to show in the bar graph and this is the expression i have used :

sum({<CalendarMonthID={">$(=vLast6Months)<=$(vCurrCalendarMonthID)"},PlanType={'Nr'},CalendarQuarter=,CalendarMonth=,CalendarFiscalYearNum=>}PlanQty)

as i am new to this ,please let me know how i need to check the condition for rev no as i have the field as rev no in my table to which this is pointing .