MDURATION(settlement,maturity,coupon,yield,frequency[,basis])
MDURATION returns the Macauley duration for a security with par value 100.
basis is the type of day counting system you want to use:
0 MSRB 30/360 (MSRB Rule G33 (e))
1 actual days/actual days
2 actual days/360
3 actual days/365
4 European 30/360
5 European+ 30/360