what is scaleleft,scalewidth etc..?

Is scaleleft position minus borders? What about textbox without borders?

Nope, Scale* properties are measured in the units you set them to. They are Twips, Pixels, Characters, etc. If you just use Width, Height, Left, or Top, it'll return the value in Twips which is default in VB. But all the APIs used Pixel mode instead of Twip, that's why it's a good idea to use Scale* after setting the Scalemode to Pixels.

Then how do you calculate the actual form area minus boeders?

I don't think borders are included when you use "Scalewidth" or "Width". So you can use these properties to get the form's actual dimensions.