Some folks want to set up their router table with a simple measuring tool, so iGaging made the analog
Multi/Mini Router Gauge Set. It was a hit, a BIG hit. People appreciated the simplicity of the original tool, but some wanted the ±0.001" accuracy that digital devices can provide. So, iGaging added digital controls and even more to their new tool, the DIGITAL Router Table Gauge.
Besides the ±0.001" digital accuracy, the tool has laser-engraved mm and 1/16 inch scales on the sides for measurements.
The digital display provides three measuring units: fractional inch (1/64"), decimal inch (0.001"), and metric (0.01 mm), with three control buttons: on/off/zero, display hold, and mode choice.
At the feet of the gauge, there are six offsets, in 1/16" increments, ranging from 3/16" to 1/2"; they can be used as set-up blocks to set the distance from the fence to the cutting edge of the bit.
The Digital Router Table Gauge has three extensions: a 1/8", 1/4", and 2" that screw into a threaded hole at the bottom of the sliding measuring scale. They also self-store in threads on top of the gauge.
Setting the center of the bit a proper distance from the fence is easy using the extensions. With the 1/4" extension, you can find the center of router bits with a 1/2" shaft (Similarly, the 1/8" extension lets you locate the center of a 1/4" shaft bit).
The 2" extension can accurately measure the distance below a surface. Lower the extension to the surface top, zero the display, and then push the probe into the recessed area you wish to measure. Simple AND accurate.
Note: When using the digital scale, before taking any measurement, you lower the sliding scale extension to the surface, then select a display mode and zero the display. You can then measure with the sliding scale. A thumbscrew locks the center sliding scale at any measurement on the scale.
Alternatively, consider the analog
Multi/Mini Router Table Gauge.