We present some results of an extensive and uniform analysis of the pl
anetary nebula nuclei from samples examined by Mendez et al. and Gathi
er and Pottasch. The present study uses distance independent diagrams.
The theoretical tracks have been modified so that they can be directl
y compared in the diagrams to the observed central star positions. Fro
m this comparison the central star masses have been derived. Our resul
ts are in contradiction with those from the above cited studies. Possi
ble explanations of the differences are presented.