Since Version 600.1401 you could use an Assistant to easily create formulas.
Before this update, you need to create PHP Scripts, if you only want to summarize some fields.
Now you create a formula, which also could be used in multiple fields.
You could open the formula assistant in the context menu of EVERY textfield, which show the small blue button on right side.
The big text field on top of the popup will get your formula with “Variables”, like Placeholders. If you want to summarize 3 fields, enter the formula Field1+Field2+Field3 and leave the formula fields with [TAB] key or something else. The assistant will parse your formula and extract every variable you use.
Now you could set the value of every variable individual. If you really want to summarize 3 fields, choose the correct fieldvalue variable within each text field.
If you click on “Save & Insert Formula” the formula will be saved and the shortcode add to the textfield you use to open the assistant. You could set a name of the formula, because in next update, you directly could assign the formula result to fields. For this you need a name of the formula.
If you want to modify a already existing formula, you need to open the task configuration, which use the formula, select the shortcode with your mouse, open context menu and click “Formula Assistant”. The system will recognize you select the shortcode, extract the ID and load the existing formula.