well I read that the 126's had this topographical sensor that works like an inclinometer that tells the trans to hold back when sitting on a hill or when descending a hill. I figure if it works on the trans it must effect the cruise. Here is a quote from Wikipedia on the 126

Drivetrain technologies
* Four-speed automatic transmission with a topographical sensor that monitored the vehicle's position (whether on an incline or decline) and gas pedal position. The result was an extraordinary capacity to "hold back" acceleration when coasting downhill and to maintain the S-Class' position without using the brake pedal after coming to a complete stop on a steep incline. The transmission also featured a "limp home mode" in case of electronic failure and was programmed to start in second gear so as to permit smooth, wheel spin free launches. Second gear start could be switched on and off in European models with a S/W switch to allow more performance orientated driving versus winter driving.
Anyway that was my question. My speedo does "tick" at low speeds though. The cruise is constantly speeding up and slowing down ever so slightly. Might be normal for all I know just doesn't seem to be the way Mercedes would design something. I had a truck once that had "Soft Cruise" to avoid that problem, it would not correct the speed in slight variations.