Feature Request: Some computational capabilities would be very nice

[ajfre]

My idea:

• Define a new field type compute

Extend existing field types:

• select: additional to the visible label, a hidden value for computation is selected
• radio: selects a hidden value for computation
• number: presents value to compute

compute contains an arithmetic expression consisting of constants and references to computational selects, radios and/or number fields and displays the result of the computation.