Cardiotron by Electro - Physical Laboratories (1940's?)

This summer I was at a yard sale and saw this Cardotron, portable EKG machine. I had to have it. I think it may be from the 40's or 50's. I also have two rolls of EKG tape. I don't really know anything about it, but it's cool. I don't collect medical devices, so it is up for sale. Make an offer.

Cardiotron, Vintage EKG Machine.