Anybody Know what this is for

[Ghoulardi]

When you have 2 surfaces that are far apart as in a large boring mill you use it as an indicator holder to keep them in line. As I was told,"any fool can get it flat, the trick is to get it in line". Last machine I did was a 40' long gap bed lathe. Took 5 months. Don't scrape any more. Too much work, and most modern machines are ground. There are still a few that use hand scraping as a selling point but its way too expensive for most applications.