Garmin E6B TAS and dalt function

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The E6B function on my 196 asks for TOTAL OAT. That means the ambient OAT plus stagnation temperature rise. If your OAT sensor is mounted in moving air, you will have some rise above ambient. How much will determine how accurate your density altitude and TAS computations are. In my plane, my two sensors are mounted out of the flow, so I only see ambient OAT. As a result, I have to do my TAS calculations in two steps. First I put in baro, altitude, and OAT and set IAS to zero, then note the resulting dalt. Then I put in the actual IAS and bump the OAT up 3C or 4C until the dalt is the same as noted. At 200 mph TAS, the stagnation temperature rise is 7.25F/4.0C. Get your total rise from (TAS mph)^2 / 5521 or (TAS knots)^2 / 4167. You may see only 50% to 85% depending on the location of your probe. If you have it mounted in your cabin air inlet, as so many do, your rise will depend on if you have the vent open or not. One way to see how much rise you are getting is to slow down to around 80-100 mph TAS, note the OAT after letting it stabilize for several minutes, then get up to normal cruise and note the new OAT. BTW; if your cabin air inlet is mounted directly in line behind the cooling air inlets in the cowling, you may be getting some air that went into the cowling, got warmed by the cylinders, and then spilled back out and flowed into your cabin inlets. I've seen that!