Calibration of 4 prototypes of sun photometers (based on Calitoo hand-held sun photometers) by means of the Langley method at Izaña and the subsequent comparison with reference sun photometers installed at this test site is a proposal led by Michał T. Chiliński (University of Warsaw, Poland) . These prototypes were designed to have 6 channels (400, 500, 675, 870, 940, 1020 nm), utilize digital viewfinder, has built-in GPS module and allows wireless synchronization with central database. The main objective of this project is to create easy to use, low-cost and reasonable accurate device for measurements of AOD, in addition to quality assessment routines, allowing unskilled users (students from different levels of education) to deliver scientific grade results of AOD measurements. In broader vision, these devices will be possible to extend AOD observations of locations where automatic sun photometer networks (like AERONET) are sparse.