Back in the 60's Aunt Maudette calibrated the speedometer with her GPS... (True name)
No sir, I have never heard anybody talk about how amazing the speedometer was. I purchased an entire cluster from an eBay member ( aresalesaz ), who bought it from a reputable rebuilder on eBay. There was a lot of communication prior to this purchase to make sure the "rebuilt" actually meant "rebuilt" with all new components. I also back-checked & fact-checked, and sure enough they did purchase a rebuilt cluster from this reputable rebuilder. The cluster's oil pressure gauge failed during my engine run-in almost causing me a heart attack, I can't get the fuel gauge to work, and now the speedometer (which I am still going to troubleshoot). I am checking the engine temp with an IR thermometer, but this gauge in the cluster seems to be OK. This aresalsaz seller did not have to respond (and does not) to my question since the transaction was older than 90 days. The cluster, complete & pretty was going to be cheaper on me than the parts & gauges to rebuild my old one, but not so cheap as to arouse any suspicion. The old cluster had mechanical temp gauge, but you all (about the same group now) talked me through what went where, etc on the new cluster.
I am sure the reputable rebuilder does fine work, and I prefer not to mention them. (edit- I just got a little ticked off about remembering the oil gauge situation- not fun at all)
Brad