Vintage Barbour Stockwell RPM / Tachometer gauge. Quality vintage USA made, they are heavy gauge chromed brass. Bezel measures approximately 9" across or so with a glass front. They were found among the collection of a retired machinist.
These are NOS, never used. Not perfect, but probably as nice as you are ever going to find.
There are other versions of these once in a while on ebay. You could take this apart and make a different face plate for some other measurement / style.
Please ask any questions first. There are 3 available, two of them are still in the original boxes with padding, and the other is loose. Let me know which you want at time of purchase.
I am not the original owner of these and have no way to try them out so being sold as found.
Good Luck