Three methods of in situ deformation modulus (Em) measurements of rock masses have been described, analysed and compared. The plate jacking (PJT) test, where the deformations are measured by extensometers 

in drill holes, gives generally the best results. A factor of 2.5 has been found between PJT and the Goodman  jack test and the plate loading test. From analyses of the results it has been pointed out that the damage from 

blasting of the test adit reduces the magnitude of test results with a factor between 2 and 4. The existing equations for indirect estimates of the rock mass deformation modulus from classification  systems have been analysed and adjustment suggested. Taking into consideration the uncertainties connected  to in situ deformation measurements caused by blast damage, test procedure, and test method, a good  characterization of the ground may give comparable or possibly better  Em  values using the RMi or the 

RMR system than the in situ tests. The RMR system gives, however, too high values for  Em  in massive  rock.