Reverse conditional sum with checkbox

I have a character sheet that I'm playing around with and would like to have the weight of armour ignored by the encumbrance calculation when a checkbox is ticked. In the wiki I found that code that includes it when ticked, but how do I do the opposite? The same checkbox is used for armour class calculations, so I don't want to break that. Code from wiki: on ( 'change:repeating_armour remove:repeating_armour' , function () { repeatingSum ( "armour_weight" , "armour" ,[ "armour_piece" ,"armour_worn"]); });

It's not as clear as it could be, I really need to rework the syntax, but you need to use the second, bigger, function on the repeatingSum page, and scroll down to Subtractions. Which is the checkbox ticked? armour_worn? I think this might work. on ( 'change:repeating_armour:armour_piece change:repeating_armour:armour_worn remove:repeating_armour' , function () { repeatingSum ('armour_weight', 'armour' , [ 'armour_piece' ,'armour_worn'], multiply:armour_worn | - 1 ); });

Thanks for the pointer, I just can't get it to work properly, which is probably more about my skills than anything else! I think the easiest route is to ensure that if the armour is worn, the weight value is manually set to zero.