Setting Formula Fields to Null

Setting Formula Fields to Null

I have two formula fields that need to be set to null in certain circumstances. 

One of those is a Formula (Date) field, and I note that I can set it to null using Newdate(0,0,0,00,00,'AM').

However the other is a Formula (Decimal) field, and I have not seen a way to set this to null. Can anyone tell me how to do this?

Thanks,

Angie