Find Minimum and Maximum values

[Inigo Montoya]

You were right Ace, declaring maxInvoice and minInvoice preserved the invoice data from one input to the next. Once I declared them outside the calculate button event, it started keeping track properly. In addition, I declared the minInvoice as MaxValue, otherwise it always had a 0 in the smallest invoice field. For anyone else needing such basic help, here's the lines I had to add:

private decimal maxInvoice;
private decimal minInvoice = Decimal.MaxValue;

Thanks again for all your help guys. I think that once I get into this a little better I won't need as much help.