Dropdown Field: No option selected points to the first Calculation value

I have a survey that calculates a donation amount based on how the user answers certain questions. The final total that gets calculated seems to be off by $10 and I can't figure out where that extra amount is coming from. I created a few hidden fields to check the sub-total amount and these all seem to be correct, however when I add them together I get a value that is 10 greater than it should be. Could you please assist?

Hi,

From what I understand to your formula, I believe the miscalculation happens because of this field:

By default, it seems that it reads the first calculation value when there is no option selected, so it adds 10 in your total field because the first calculation value is 10.

To fix it, what you need is add a "0" value as the first one in the list. Here's a screenshot of it:

That should fix it. Let us know if it works.

Thank you.