This probably shouldn't be a single text field formatted with check boxes but rather a set of related records. Then a field in each record can record the numeric value and Sum ( RelatedTable::NumberField ) can return a total.
The problem with using a single check box field is that when multiple boxes are selected, the value of each check box is inserted inthe field, separated from other values by a return character. This makes it tougher to "add up" the value of just those selected values.
On method is to use the FilterValues function to test for whether a given check box is selected or not. Say your check box uses a value list of three values: "Red"; "blue" ; "yellow".
You might set up something like this:
Let ( CB = YourCheckBoxFieldHere ;
If ( Not IsEmpty ( FilterValues ( CB ; "red" ) ) ; 1 ; 0 ) +
If ( Not IsEmpty ( FilterValues ( CB ; "blue" ) ) ; 5 ; 0 ) +
If ( Not IsEmpty ( FilterValues ( CB ; "yellow" ) ) ; 10 ; 0 )
But note how much more complex of a solution this is and how you'll have to redesign this calculation every time the list of check box values or their associated numeric values need updating in the future--neither of which is much of a problem if you use related records in a portal instead of your check box field.
And it's possible to list your different values in a portal that looks and acts like a check box, but which now has both a scroll bar and which can be sorted in ways not possible with the standard check box field. For multiple examples of this approach, see:
thanks, I only have one field that can require multiple values. The rest are either yes or no values