A method for quick and pretty accurate measurements of splay, twist and bend elastic constants of nematic liquid crystals is proposed. The main concept relies on exploiting only electric field in a plane-parallel liquid crystal cell of special configuration with thin transparent comb-like electrodes on one cover and usual transparent plane electrode on the other. Rubbing in direction parallel to comb electrode stripes enforces homogeneous planar or homeotropic orientation of nematic molecules. Freedericksz' transition of pure splay, twist or bend form is initialised by applying voltage between the electrodes appropriately. The method was tested with three different comb-like electrode configurations and three nematics: 4-pentyl-4'-cyanobiphenyl, 4-trans-4'-n-hexyl-cyclohexyl-isothiocyanatobenzene and Demus' esters.