Unusual lever on pressure regulator thumb screw
 

Has anyone ever seen this lever on the pressure regulator and do you know what it does?
Any ideas on how to use it?
Thanks for your help.

I THINK if you push the one round plunger down for pressure, you can lift it up by holding the finger down. be careful, it might hurt you if it flips back up. I have one something like this on one of my machines. I don't know what the screw part does. It probably holds the pressure down, after you push the plunger down. Not sure.

I think Miriam brought this up sometime in the past year. As I recall it is a release tab. I've never seen or worked with one.

Yup Elian is right on all counts
Some times that kind works well some times not

This is on a Singer 66 issued July 28, 1927. On the tab it says "Patent Revco Pending".
Fascinating...I'd never seen one before.

I'm thinking those were an add on thing you could buy.

Yes they were, just like the aftermarket Revco reverse add on.

Cari

I would like to see the rest of the machine. That was an upgrade at some point in the machine's life. I'm wondering if it also got the Revco reverser at the same time.
Rodney

Looks like it works like one of those hold open gizmo's on the screen door "closers"....trying to understand the draw of such a thing? Who adjusts the presser foot tension enough that a couple twists is that big a deal?