However, the theoretical predictions in resolving power of the VFDT were much higher than what was observed experimentally. 
the VFDT
The HVP-VFDT atmospheric pressure portable system improves the resolving power from the maximum expected of 60-80 for a regular drift tube to 250 in just 21 cm in length and 7kV, an unprecedent accomplishment.
the HVP-VFDT atmospheric pressure portable system