Form Calculator is not calcuating values correctly

I've created a form, but the field calculator does not seem to be working properly. I have two dropdown where I assigned various quantities to the options. I want to some the value of the two dropdowns in a form calculator field. However, the form calculator automatically starts with 25, and I don't know why. Also, the numbers that are added in the field calculator aren't the same as the ones that I have declared in the calculation values. Thanks a lot for any help!

The default value 25 is shown because it is calculating the first values. The default calculation can be avoided by selecting the option "Wait for input before including the field in calculation" in Calculation Wizard.

The calculations are not expected due to the options on dropdown are considered as 5 values includes blank option instead of 4.

To resolve this issue, please add 0 to the calculation values in the beginning for the dropdown fields. 

Hope this information helps. Please get back to us if you need further assistance. We will be happy to help.