Simple Subtraction, incorrect answer. Help!

Okay, I am simply trying to test my form, here's my example: I have 100,000 in 'FieldOne",  800,000 in 'FieldTwo', and the following script in the answer field:

var a = +getField("FieldOne").value;
var b = +getField("FieldTwo").value;
event.value=a-b

And the answer I'm getting is -700,000.

On the flip side, when I try addition the answer is 900,000.

This is totally bizarre and so frustrating. How do I fix this?

TIA