There are numerous ways to get a level baseline on glassware for your letters. The same item works flawlessly for a circular line around a plate. Thanks to Fred Ortiz, one of my successful students in far south Texas for this idea. HOBBY LOBBY has this compass for around $18. in their art department. Be sure it has the fixture for using a marker. Works great!
A word about the collection plate. A woman in a nearby Texas community Googled for someone to engrave a couple of commemorative offering plates, honoring her parents. My name came up. The compass made fast work of the arcs I needed. The line on the top of the plates had its base line; the line on the bottom had a different one.
The challenge on this job was getting the bottom line centered below the top one on each plate. Multistep process that worked nicely. I had about 25 minutes total in each plate. Charged her $100. for each plate and she was thrilled with the results and price. Those plates will probably be passed around the pews in her little church for decades to come.
They were made of extremely light and hard metal…not sure what. So hard, I had to use a brand new #6 round carbide bur for EACH line to keep the letters deep enough to be consistent.