Serial numbers were pressed into the rear of the removable lid, the cabinet, and the front panel insert of each CT-100. The number 605 appears on my set. Below, the picture of CT-100 lid and cabinet number 600 comes from another Merrill whose chassis serial number is, like mine, below 1000. It's entirely possible that nearly 50 years ago these two cabinets were within a few feet of each other at Bloomington. --Pete