I have just made an excel sheet to calculate whether or not to call on a draw (situation dependant of course).
Could someone check the following formula for mistakes please.

Before turn: (outs/47)-(Amount to call/Total Pot)
Before river: (outs/46)-(Amount to call/Total Pot)

I made the simple tables just for personal use but if anyone would like I can send it to you via e-mail.

Thanks for your help :-)