I learned a very neat trick yesterday. You ever get 'inconsistent units' as result from a formula? For instance if you wanted to multiply moolah with area with integer with bingzoombang? There's one real obvious way to make everything unitless.
Example: =(Cost/1$)*(Area/1m²)*(bingzoombang/1bzb)
Or in other words, just divide the parameter with one instance of it's own unit. The order in which you process everything will make a difference too, but if you really hit this one snag and don't have time or a superbly overflowing know-how to solve it 'the right way', make it unitless and you'll get the right result every darn time.
1320mm/1mm = 1320. 8ft/1ft = 8. 1320 sq.ft/1sq.ft = 1320. $1,836,249/$1 = 1,836,249. Easy like that. It's not even a workaround, it's the right mathematical way to go around with processing numbers.
Now suppose you have a formula and only want one parameter to be interactive. Height = Length / 2 will make both interactive.
You can add a dummy parameter, but that's just clutter. My way: Height = if(Length>0, Length/2, 0)