Wild RDS self-reducing tacheometer.
The Wild RDS Self-Reducing Tacheometer gives a direct horizontal distance reading and a height difference involving no tables and only a simple mental multiplication. Based on the TI6 theodolite, the RDS is used with a vertical staff and the normal stadia lines are replaced by very flat curves. When the special RDS staff is used, its zero mark is set to the same height as the tilting axis of the instrument, thus making calculations even easier. The RDS can be used as an ordinary theodolite, with the normal TI6 reading accuracies. (ref: Virtual Archive of Wild Heerbrugg http://shop.wild-heerbrugg.com/index.php?cPath=1_3_5_25_65&MODsid=912fe990c9357dc03e5640fbfd3795bb.)
It was manufactured by Wild between 1950 and 1989.