Nielsen7 / Big Holes

This is distinctive because of the very large holes drilled in the top, bigger than other holed computers from the Nielsen Electronics Institute.  

It's also interesting as it's the only CTI labeled computer, which also has the later CTI produced circuit board, and it has the serial number "501" suggesting CTI used a different serial number sequence for computers they made.  Other CTI machines may have serial numbers, but it's hidden under a round white paper label.   (Nielson8 is CTI branded, but has a definite earlier Kenbak assembled PC board, and is serial numbered 203)