Top panel: corrections to the WD masses determined using zero temperature WD mass-radius relation (Nauenberg 1972) depending on the hydrogen envelope temperature. Differences between WD masses found using hard X-ray observations (Suleimanov et al. 2019) and using optical methods for four objects are also shown. The difference between the average WD mass in IPs and all the CVs (Zorotovic et al. 2011) is shown with the pink dot. Bottom panel: corrections to the WD masses determined using the Nauenberg (1972) mass–radius relation (2) and numerical M − R relations obtained by Hamada & Salpeter (1961) for different WD chemical compositions.