Lab. assignment No. 4 for Measuring systems in computer engineering course at the University of Belgrade - School of Electrical Engineering (http://automatika.etf.rs/sr/13e053msr) in 2020 and 2021 (it was No. 9 in 2017 and 2018, and No. 7 in 2019). Author would like to thank BSc students - demonstrators Uroš Kukić, Dušan Prokić, Pavle Radojković, Bogdan Badnjarević, and Nikola Valzorio for their valuable feedback for assignments improvements. Also, special thanks to BSc students in school year 2021/22 Marina Zlatković, Filip Starčević, Sonja Grubor, and Vladimir Janković.