12" Electronic Digital Calipers

It's not a ruler. It's not measuring tape. It's a micrometer! Yeeha!

This really is an excellent tool. You'll never go back to an ordinary ruler once you have one of these. It's just so much easier and more accurate that you'll wonder why you didn't go for one earlier, especially since they're available for pretty low prices all over the web.

Above is the case. It's plastic with a wood grain pattern. There's no latch, but it requires a bit of force to click it open or closed. Below is the interior, with the instructions, guarantee, calipers, and spare button cell. It's quite a decent case.

Below, you can see the main O.D. jaws, the auxiliary I.D. jaws in the rear, the electronic body, the small locking screw, and the larger adjustment wheel.

• The main jaws are for measuring ordinary lengths, or for outside diameter of tubing and such.
• The auxiliary jaws, which have flat edges on their reverse sides as compared to the main jaws, are for measuring inside diameters. They're more useful than you'd think, as they're not just for pipes.
• The electronics are what makes this such a handy tool. The blue "inch/mm" button switches the current measurement from SAE to metric and back. "in" or "mm" appears on the display. The red "OFF/ON" button turns it on and off (duh). The yellow "ZERO" button resets the zero point. You can zero the tool at the actual zero to use it as ordinary calipers, or you can do it with the jaws open, to add or subtract lengths. If you zero it and then close the jaws, the display will simply use negative numbers.
• The small thumbscrew at the top can be used to tighten the jaws in a specific place so they're not quite so susceptible to bumps.
• The large adjustment wheel on the right is used to widen or close the jaws with one hand. Press the wheel lightly into the ruled area and push it forwards or pull it backwards to adjust the tool's movable segment.

There's also a depth measurer. I haven't used it too often, but it was nice to have one when I wanted it.

Of course, you can use the ruled area without the electronics to make quick measurements.

These things are available in a wide variety of sizes, from 4" to three feet or more. The small ones are usually quite inexpensive, at $20 for a 4" or 6" model and around $30-40 for a 12" like this one. I got mine from an eBay store, and I feel that I got a great deal.

Get some electronic digital calipers. You'll be really glad you did.