When you need to measure cutting height rather than depth, Rockler’s $59 Digital Height Gauge is ideally designed for the task. Essentially, it’s a caliper with one jaw removed and mounted to a heavy steel base. The indexing jaw is also overly thick to provide an ample reference surface. To use the device, lower the jaw to a tool table and zero it out. Then, choose your readout option and roll the thumbscrew to raise the jaw to the desired height. Readout is constant as you go up. It will extend up to 6".
Here’s a gauge that should prove valuable for setting the infeed table of your jointer without relying on the machine’s crude scale or using a feeler gauge and straightedge. Or, set the jaw over a bit in the router table and use the LCD to find the precise cutting height you need while you crank the bit up. A lock knob on the Height Gauge can hold the position if you need to return to the same cutting height again.