Discontinued and relatively rare.
Blue Plus model Cellidor scales with an Telemehanique inlay.
Engineer is a collectors name for this model as it's unknown if an official name was ever given to it.
The Engineer was a special run made in the late 1980s for a French industrial control company called Telemecanique for users of the Altivar 5, a motor speed controller typically used in industrial automation settings (assembly lines, etc).
If you look inside an Altivar 5, you can see why the technician screwdriver is the perfect tool to give out with it. There is a row of grey screw-type wire connectors on the left of the upper PCB and across the bottom of the lower PCB for wiring the motor up, and the screws are recessed into the connectors. Also, there are 6 adjustment potentiometers on the upper board and 12 dip switches.