Normal is between 40 - 130 on a human glucometer.
The lowest you want your cat to go between shots is 50 mg/dL on a human meter if following a Tight Regulation protocol; 90 mg/dL if following the Start Low, Go Slow protocol. This gives you a small buffer zone to accommodate the +/- 20% variation which is FDA-allowed in home glucometers.
See my signature link Glucometer Notes for more details.