Instructables
Picture of Make a diving depth gauge
Frustrated by lack of cheap analog depth gauges around, I've decided to make my own. It turned out that it was very easy  to do so and gives appreciable result. So here's how to make a capillary type gauge that's relatively accurate up to 30 meters (100 feet) for about $1.

Sorry for the poor image quality. I may replace them someday, but I think these are good enough to illustrate the process.
 
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Step 1: Materials

To make the gauge, the first thing you will need is an ink tube from a ball-point pen. You could use any other piece of thin clear tubing, but I used a ball point pen tube. You need one that's straight, clear and as long as possible. It's diameter should be around 2 -3 millimeters (a tenth of an inch), bigger diameters will not work.  The tube will be the core of the depth gauge.
The next thing you will need is a piece of a hard flat ruler to glue your scale and tube to it. You will also need some epoxy resin and/or a laminator to glue and waterproof the printed scale, but I recommend you use both. You'll probably need a syringe, a syringe needle and some lighter fluid to clean the tube from the ink.