Frame rate is effectively inversely proportional to the rate of change and the amount of work your graphic card is being asked to cope with. In drive most of the time the change is quite gentle, and unless you are swapping between internal, following or trackside views, the changes are little more than a view gradually panning across the screen. However in surveyor you are manually controlling that movement, often quite deliberately moving back and forth across your creation, frequently zooming in and out and so forth making rapidly changing to what's on the screen and the workload on the graphics card, hence the resulting reduced frame rate. Resolvable with todays a high end graphic card should it be sufficiently annoying although unlikely during editing, but still an interesting observation. Peter
