We picked up a Stanley Sweetheart No. 13 level today at a yard sale. It is
26" long. The center horizontal bubble is missing (was it ever there?).
There are two vertical bubbles. There are no patent dates on the brass.
There are brass end corner caps, but not across the entire end.

I can't find a similar level on eBay or anywhere else, and certainly not to
a No. 13.

Anyone know anything about this level, age, etc., or where I can learn about
it?

And, yes, I have Googled it.

This is really on the level.

George