Considering the snapshot below taken from my Configure Customer Units dialog I will try to explain how you can configure Screen Calipers to measure "feet" in 2 ways. But this example applies to configuring any other unit. Here is the snapshot:



And now the explanation:

When starting to define a new unit, the most import thing is to know how many pixels per inch does your monitor support. In my case if I look at the second row (the one where Inches is defined) I see that the Number of pixels for 1 inch is 96. So my display monitor supports 96 pixels per inch. This is a readout the above dialog gives you automatically but please noticed that this may differ in your case.

Starting with this reading we can define any measurement unit we want.

There are two cases for configuring Screen Calipers or any of the other screen measurement tools:

First case:
Suppose we want to define feet as a new measurement unit: we know that 12 inches represents 1 foot. Then we do the calculations below:
If 96 pixels represents 1 inch
How many pixels represent 12 inches
The result is that 96 pixels * 12 = 1152 pixels represent one foot.
This is the case of the "foot" measurement unit defined in the snapshot above. This case is the case where you have large scale drawings in which 1 foot in the drawing represents 1 foot on the screen. But usually the drawings you want to measure aren't that big, I mean there are usually smaller scale drawings in which you know that a certain part (a door for example) measures 2.75 feet and here comes the second case to help you measure smaller scale drawings.

Second case:
You have a small scale drawing for which you know how many feet an object of your drawing has. Suppose you have a small scale drawing of your house and you know for a fact that your door measures 2.75 feet. Then you use Screen Calipers to see how many pixels are shown for that door. Suppose you obtain 30 pixels. Then you know that the "Number of Pixels" your door has is 30 (you enter this in the "Number of Pixels" field) and you know that the "Length in Units" field has 2.75 feet (you enter this in the "Length in Units" field). Then you enter the name of the new unit as you want (I've named it "foot when knowing real measurement").

This goes for every new measurement unit you want to set up in Screen Calipers or any other of the measurement tools Iconico offers.