Maybe this should be posted in the Bicycle Mechanics forum, but I thought I would put it here. On Thingiverse I found this replica of the Jobst Brandt Tensiometer,
https://www.thingiverse.com/thing:2810089
Attachment 606660
Then I decided to make one for myself. I had to modify the original model to fit the more readily available parts here in the US, most bought from Amazon, if anyone wants to build their own my source files are available.
Attachment 606659
Without proper test equipement the tool is not calibrated to directly read spoke tension, but it can read a consistant number at a given spoke tension, so it can be used after the wheel build to test for evenness of the tension. Here is a list of parts I used from Amazon.
The model source files can be found here,
https://a360.co/2JC6Jwe. It is a bit larger than the one on Thingiverse to accomodate the Amazon supplied hardware. It works. With the same spring you will get about a 1 mm deflection of the spoke when the spring is decompressed.
Here is how I printed this; PETG filament, 30% infill 3 perimeters, printed on a Robo3D R2 printer. Since this is just a tool pretty much any type of filament will work. Every piece was printed in the orientation directly from the source, only the channel for the linear rail required supports. With a shorter rail this could have been built smaller, but I was finding that any rail shorter than 100 mm really shot up the price, so I settled on the 100 mm size.
I have been using it about a week now double checking some of the wheels I have built in the past. It is not the easiest tool to use but I can vouch for the fact that it is a great way to test the precision of your wheel builds. Full disclosure, the wheels I checked were built using the Park Tool Spoke Tension Meter (TM-1) so I already knew they were pretty even in tension from spoke to spoke.
One last note, I did not print the spacer, I removed the back of the dial indicator and screwed the indicator (sans back cover) directly into the base of the tool.