Due to the obsolescence of software, constant update of reference laws and failures that may affect electronic boards, if often occurs that measurement instruments, even sophisticated ones like roundness testers, are still in good operating conditions with regards to the mechanical aspect, but are no longer suitable to perform characterizations of pieces. SM retrofit kits were conceived from this need, developed thanks to the extensive experience in the sector of industrial metrology. The roundness tester retrofit is carried out by replacing the instrument’s existing electronics with one of new generation, that is connected with the same cables and connectors to the mechanical part of the roundness tester containing actuators and sensors. The instrument's update is concluded by installing the Circom software to analyse geometries, that is interfaced to the new electronics through USB. The retrofit of an old roundness tester can be considered an excellent alternative instead of purchasing a new instrument, because with a limited expense, you can restore a device that will be comparable with a new one, once updating is completed. It is also possible to request the cleaning and complete inspection of the mechanical parts of the instrument, performed by highly qualified staff. The retrofit kits are divided in three categories, according to the level of movements of the machine to upgrade. 5.100 Retrofit Circom base (Manual enabling of only the plate, column, R arm). 5.101 Retrofit Circom full (Manual enabling of the plate, column, R arm). 5.102 Retrofit Circom plus (Enabling of the plate, column and R arm).