This function allows you to take a drawing that was printed out of scale and measure it as though it was perfectly to scale. This is made possible by using the sliding pointer. Line up the start of a known dimension (point A) with the fixed pointer. Move the slider to the end of the dimension (point B). Input the distance it represents, your desired units and hit enter. The screen will regenerate itself to the new custom scale.
This function allows you to convert the screen between metric and imperial. For example, if you've received a drawing in imperial, and you're more comfortable with metric, tap the convert button and the long screen regenerates to the metric version of whatever was on the screen previously, or vice versa.
This function is is applicable when you need to divide a space into a number of equal sections. For example, if you have to make 4 equally spaced lines on a drawing, instead of working out the math separately you simply follow the same steps as the with the custom scale section above. Move the sliding pointer across the distance that requires dividing. Input 4 on the number pad and the ruler will display 4 equally spaced notches on the screen.