A depth gauge is a tool that helps measure the distance from the surface or top to the bottom of something. It is commonly used to measure the depth of water or the depth of cuts in woodworking or metalworking. Full definition
You might wonder why I'm talking about mechanical depth gauges in an era of high tech computers which are doing the same job more accurate with just a sensor. (dive-internships-bali.com)
Pumpkin Digital Tyre Tread Depth Gauge Range at 0 - 25.4 mm with Large LCD Display Inch / MM Adjustable Tread Depth Measuring Tool for Motorbike Car Van (amazon.co.uk)
Contact Seller 2010 Sun Tracker Regency Edition, Features include 115 HP Mercury motor with hydraulic trim, dual axle trailer, full width swim platform w / fold down ladder, padded sundeck w / pop - up changing room, freshwater sink, compass, navigation lights, digital depth gauge with water temp, Satellite radio capable AM / FM / CD stereo w / MP3 jack, canvas boat cover, table and wheelchair access gate. (smartmarineguide.com)