ClearNav does not need a variometer, although of course the pilot does. ClearNav is a navigation, airspace, glideslope and task management tool which works quite independently of any and all variometers.

ClearNav uses a highly reliable and extensively tested algorithm to determine windspeed and direction from wind-induced drift while circling and it uses GPS height information to determine the average climb for the current thermal and the average climb since starting the task.

ClearNav does not provide speed-to-fly (STF) information. Although GPS height data is good enough to allow an accurate measurement of average climb rates, it is not good enough to provide speed-to-fly feedback. That job must be done by a variometer.

The choice of variometer for ClearNav users continues to generate numerous questions and considerable confusion. All STF variometers require that the user enter a MacCready (MC) value and so, for fundamentally different reasons, does ClearNav. The vario needs the MC value because STF depends not only on the rate at which air is rising or sinking, but also on the chosen MC value. ClearNav needs a MC value because the glideslope information to the active waypoint (and the amoeba) obviously depends on these values. There are good reasons for flying with both the vario and CN using the same MC value, and equally good reasons to use different MC values for each.

Variometers produced by Cambridge Aero Instruments are unusual in that they compute windspeed and direction and make it available to external devices. The Cambridge “Vector Wind” calculation requires that the glider change track, something accomplished either by circling, or by a zigzag maneuver. In practice Vector wind values and ClearNav circling wind values are in good agreement. Many CAI users prefer however to use the vector wind value and NK makes this easy by providing a cable which connects a CAI 302 or CAI LNAV/GPS-NAV to a ClearNav. When this cable is in place the ClearNav is forced to display CAI vector winds, and will take control of MC, Bugs, and Ballast settings in the 302 or LNAV. All changes made to these settings on the ClearNav will propagate to the Cambridge system. Any changes made to the Cambridge settings do not propagate back to the ClearNav thus one can fly with different MacCready values if desired.