The security problem of screen image leakage from a display unit through electromagnetic (EM) radiation has received wide interest of security researchers since the Van Eck's paper. To investigate the risk of EM-information leakage, we want to analyse as many devices as possible. However, during the evaluation, we face the problem of necessity on the target devices' synchronization parameters which we use to reconstruct the image. Even though limited numbers of timings are used in the field, slight differences among devices introduced during production require an evaluator to search for the actual timings for each of them. The search has been done by human heuristics and many trial and errors; which prevents analysis of massive amount of target of evaluation (TOE). We propose a technique to automate the search by using a classification method, which is carried out on a computer, to help EM-leakage evaluation.