DISC(settlement,maturity,par,redemption[,basis])
DISC calculates and returns the discount rate for a security. settlement is the settlement date of the security.
maturity is the maturity date of the security. par is the price per $100 face value of the security. redemption is the redemption value per $100 face value of the security.
basis is the type of day counting system you want to use:
0 US 30/360
1 actual days/actual days
2 actual days/360
3 actual days/365
4 European 30/360