An old Sunnen torque wrench model PN-50, how old? Does anyone remember them?

I came across an old Sunnen torque wrench, the model number PN-50. I wanted to know if anyone remembers them? Also how old do you think it is? It has like a little arm that folds back onto itself from the end where you place the socket. That is hard to explain, they need to use pictures on here. Thanks