Measuring a sealed unit thickness

Double glazed units have variable size thicknesses, to measure this without deglazing for replacement needs a special tool to measure around the frame profile.
A commercial tool is available but for a one off its not worth it.
Attachment 47578

A simple mod to an outside caliper using an eccentric disc will do the same job.
Attachment 47579
Clamp the caliper on the glass, rotate the disc and lock it, after removal the caliper can be closed to the disc retaining its original position.

Attachment 47580

Height and width are typically minus 10mm from the frame bead joint.

<!-- BEGIN /var/www/html/homemadetools/protected/modules/zeus/views/tool/postUpdate.php -->
Thanks olderdan! We've added your Thickness Caliper to our Measuring and Marking category,
as well as to your builder page: olderdan's Homemade Tools. Your receipt:

<div id="blocks"> <div class="block b1 pngfix"> <div class="bimg"> <div> <a href="https://www.homemadetools.net/homemade-thickness-caliper-26"> <img src="/uploads/269003/homemade-thickness-caliper-26.jpeg"/> </a> </div> </div> <div class="head pngfix"></div> <div class="left pngfix"></div> <div class="right pngfix"></div> <div class="blockover b1 pngfix"> <div class="title"> <a href="https://www.homemadetools.net/homemade-thickness-caliper-26">Thickness Caliper</a> <span> by <a href="https://www.homemadetools.net/builder/olderdan">olderdan</a></span> </div> <div class="tags">tags: <a href='https://www.homemadetools.net/tag/thickness-gauge'>thickness gauge</a> </div> </div> </div> </div>
<!-- END /var/www/html/homemadetools/protected/modules/zeus/views/tool/postUpdate.php -->

Despite seldom having to make obstructed measurements like this, I like this idea of resettable calipers. I can think of a few other uses for this added feature. If one has calipers with a screw adjustment, adding a stop nut to the threaded rod provides this refinement.

Other approaches to the problem...

Measure across a block held to one side of the glass. The block must be large enough to force the calipers to be opened far enough to clear the obstruction. Subtract block width from caliper measurement.

Simply open the calipers far enough to clear the obstruction and measure their opening. With one arm against the glass, measure the distance of the other arm from the (other side of) the glass. Subtract the latter measurement from the former.

Simplicity at its finest. Great idea !

A good idea with application for other measuring tools. So simple yet so effective (why didn't I think of that). Thanks.