At Catalyst fitness last July I was doing arms on Thursday and found they had a Hammer Strength Bicep curl machine. My old gym had the same machine. It was funny to see a weight plate under the lower floor support arm.  This raises the handle an inch or so the user doesn’t have to lower it as far down.  I don’t know the exact reason you would do this – perhaps you have elbow issues and want to alleviate strain on them.  Maybe you want to keep constant pressure on your biceps and this is how you do that.  When I used the one at Spiece, there would always be a weight plate in the same place under the support arm on the floor. 

I used to leave it there and now I remove it so my arm range is far as it can extend.  Do you have a machine like this at your fitness center?  Do you or others put a plate under it, too?  It’s funny how both gyms do the same thing on this machine.