Based on the 10th photo, I believe this was manufactured in 1979. It's an early BOSS model, so the LED only lights up when you step on it (it doesn't stay lit when ON). The yellowing on the back is from adhesive used to attach Velcro. The silver screw is bent, but it doesn't affect the operation. ● Serial Number: 8600 ● Op-amp: NEC C4558C ● Silver Screw