Tired of trying to measure long pieces accurately I ended up getting a long (600mm) caliper. What a difference it made. As most everything else in this project, I found it on eBay. I got it from someone in California but it obviously came from China. Given that it is a copy of a $860 Mitutoyo for about 1/5 of the price, it’s a great bargain. It performs well and I am surprised by its accuracy and repeatability.
The eBay seller goes by “ISoldIt”. If they are around or not by the time you try the link I can’t tell. These eBay sellers all seem to be quite sporadic. If you can’t find them, just look for “600mm digital caliper”.