Semi-technical, not perfectly accurate explanation follows:Keep in mind, as well, that we're dealing with mechanics here. We're using the differential pressure between the static reading and a ram air reading (via the pitot tube). In order for it to withstand higher ram air pressures, the wafer needs to be reasonably thick. Because that wafer needs to be thick, it only starts to compress at a certain speed.Take a look at a Cessna panel. Where does the airspeed pick up there? 40 knots.Furthermore, as alluded to above, speed indications less than necessary for flight are really worthless to me. Taxiing is supposed to be a judgment call on the part of the pilot (by way of vision - there are no set speed limits on the ground, really), and even so, most manuals would tell you to use the GS indication if knowing your speed is truly necessary. All that said, there's no reason to make pitot-static systems sensitive enough to pick up such low speeds.

Semi-technical, not perfectly accurate explanation follows:Keep in mind, as well, that we're dealing with mechanics here. We're using the differential pressure between the static reading and a ram air reading (via the pitot tube). In order for it to withstand higher ram air pressures, the wafer needs to be reasonably thick. Because that wafer needs to be thick, it only starts to compress at a certain speed.Take a look at a Cessna panel. Where does the airspeed pick up there? 40 knots.Furthermore, as alluded to above, speed indications less than necessary for flight are really worthless to me. Taxiing is supposed to be a judgment call on the part of the pilot (by way of vision - there are no set speed limits on the ground, really), and even so, most manuals would tell you to use the GS indication if knowing your speed is truly necessary. All that said, there's no reason to make pitot-static systems sensitive enough to pick up such low speeds.

besides the fact that airspeed is not meant to tell you how fast you are moving, rather the amount of air that the aircraft and her wings are penetrating. Thats why your airspeed would decrease as you climb into thinner air if you were to maintain the same forward speedEric

besides the fact that airspeed is not meant to tell you how fast you are moving, rather the amount of air that the aircraft and her wings are penetrating. Thats why your airspeed would decrease as you climb into thinner air if you were to maintain the same forward speedEric

Indeed, your airspeed is your speed relative to the air, when you're taxiing you need your speed relative to the ground. If your plane is parked with the nose into a 20 knot wind your airspeed indicator will say you're doing 20 knots (assuming it was capable of indicating below 45 kts), even though you're standing still with respect to the ground.If your airspeed ever reaches lower than 45 knots in flight, then, as they say on the internet, you're doing it wrong!