Let's say I have Control1.Height = 200
i see what it does but i don't know what it is
So a control with height 200 would be 0.5" tall on a device with 400 ppi, is that correct?
i would say it depends.
as you mention ppi, i believe you are talking about a mobile device.
mobile devices use 'View port' resolution rather than true physical resolution.
I like to chuck a couple of temporary labels somewhere on the screen with text properties as per below.
You can then keep an eye on the screen dimensions your working with and set various elements to values that relate to them and to other element properties. ie making sure components stay visible instead of being pushed off the screen on a mobile device when changing orientation.
" App Width: "& App.Width&" Size: "& Screen1.Size & "Gal Width " & Gallery1.Width
" App ht: "& App.Height&" Size: "& Screen1.Size& " gal ht: "& Gallery1.Height