100 200 50 150 Ram air Static air line Pitot tube Long lever Sector Handstaff pinion Diaphragm Pitot connection Figure 5-11. Mechanism of an ASI. Types of Airspeed Indicated Airspeed (IAS) Calibrated Airspeed (CAS)  Equivalent Airspeed (EAS)  True Airspeed (TAS)  Just as there are several types of altitude, there are multiple  types of airspeed: indicated airspeed (IAS), calibrated  airspeed (CAS), equivalent airspeed (EAS), and true airspeed  (TAS). IAS is shown on the dial of the instrument, uncorrected for  instrument or system errors. CAS is the speed at which the aircraft is moving through  the air, which is found by correcting IAS for instrument  and position errors. The POH/AFM has a chart or graph to  correct IAS for these errors and provide the correct CAS for  the various flap and landing gear configurations. EAS is CAS corrected for compression of the air inside the  pitot tube. EAS is the same as CAS in standard atmosphere  at sea level. As the airspeed and pressure altitude increase,  the CAS becomes higher than it should be, and a correction  for compression must be subtracted from the CAS. TAS is CAS corrected for nonstandard pressure and  temperature. TAS and CAS are the same in standard  atmosphere at sea level. Under nonstandard conditions, TAS  is found by applying a correction for pressure altitude and  temperature to the CAS.  Some aircraft are equipped with true ASIs that have a  temperature-compensated aneroid bellows inside the  instrument case. This bellows modifies the movement of  the rocking shaft inside the instrument case so the pointer  shows the actual TAS.  The TAS indicator provides both true and IAS. These  instruments have the conventional airspeed mechanism,  with an added subdial visible through cutouts in the regular  dial. A knob on the instrument allows the pilot to rotate the  subdial and align an indication of the outside air temperature  with the pressure altitude being flown. This alignment causes  the instrument pointer to indicate the TAS on the subdial.  [Figure 5-12] 120  130  140  150  2  4  6  MPH  TEMP  30  30  0  + -  AIRSPEED  TRUE SPEED  KNOTS  I80  40  60  I60  80  I00  I20  I40  40  I40  I20  60  80  100  Figure 5-12. A true ASI allows the pilot to correct IAS for  nonstandard temperature and pressure. Figure 3-12. A true airspeed indicator allows the pilot to correct indicated airspeed for nonstandard temperature and 5-9