For setting precise plunge depth on my router, I often use a gauge of the same thickness as the desired routing depth.
Micro-Adjust Plunge Depth Without an On-Board Scale
Hammerhead 10-Amp Variable Speed Plunge Woodworking Router Kit with Parallel Guide and Vacuum Adaptor – HAPR100 : : Tools & Home Improvement
T14 2300W Variable Speed Workshop Plunge Router
Adjust blade depth to your stock thickness
This precision gauge has an angled display for easy viewing as well as auto shut off. And it fits most portable woodworking planers. It easily
Wixey WR510 Electronic Digital Readout Kit for Portable Planers
Micromachines, Free Full-Text
Professional Results with Festool TS 55 FEQ Track Saw
Veritas Plunge Base for Rotary Tools Set - Lee Valley Tools
2 Peak HP Plunge Router - RYOBI Tools
Goofproof gauge blocks for thickness planer