How to set the Form Calculation widget to Read-Only?

https://www.jotform.com/build/72478287684171

MOST of our members are over 55.  Some are computer literate, some can read (kidding), AND some don't seem to know how to fill out a form.  It would help if the calculated total field was ONLY FILLED IN by the total of either/or both of the two fields (membership dues, donations) instead of the member being allowed to fill in whatever he/she wants.

I've looked at the options/widget but I don't see away to STOP them from putting in whatever they want...we can't "force" either of dues/donations fields because they might not want to pay dues (just donate) or vice versa.

Please tell me there's something I've overlooked and that I can somehow restrict the member from filling in the field.  Just prior to typing this request...I changed the 'Correct Amount? If yes, Pay Below' to read "PLEASE DO NOT TYPE IN AN AMOUNT HERE" and tested to see that it was replaced with $10 when I chose a $10 dues.

We would still like them NOT to be able to change that field, as this is the field that fills in the PAYMENT amount in the next form question/field.

Thank You.

You can set the Form Calculation widget to be Read-Only. This can be done inside of the widget settings.

Here is my demo form: https://form.jotform.com/73251435470957 

Feel free to test it and clone it. 

Let us know if you need further assistance. 

THANK YOU!!!!!!!!  You guys have fantastic customer support!