If you're still measuring, marking and drilling large numbers of mounting holes without the aid of a device like this, you're wasting a lot of valuable time.
Here's how it works:
Reset the raised ledge on the back side of the Easy Mark on the top edge of the drawer front
Slide the horizontal stop all the way to the right and center the device on the drawer front, using the left and right half-scales as indicators
Slide the stop to the left until it makes contact with the right side of the drawer front and tighten
Adjust drill bushings (3" to 4-1/2" on-center) to match hardware mounting holes and tighten
Loosen the locking knob on the drill bushing block...slide it vertically to your desired postition...and re-tighten the locking knob
Use a 3/16" twist drill bit in the applicable hardened bushings to bore mouting holes
Move the Easy Mark to the next drawer and repeat the process