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of the glider is higher than the indicated altitude. Fortunately, this error can be corrected by setting the altimeter properly. When flying in the local area and communication with ATC is not available to provide the current altimeter setting, there is an alternative procedure. Set the altimeter on zero while on the ground to directly read AGL referenced to the landing zone. However, for cross-country flights and flights from higher elevation airports, that procedure may not be an option due to the excessive Kollsman window setting instrument required. In those instances, the altimeter can be set to read the field elevation and either disregard the Kollsman window setting or applying a correction factor, or set in the barometric altimeter setting and remember if it reads high or low. 

Variations in air temperature also affect the altimeter. On a warm day, the expanded air is lighter in weight per unit 

volume than on a cold day, and consequently the pressure levels are raised. For example, the pressure level at which the altimeter indicates 10,000 feet is higher on a warm day than under standard conditions. On a cold day, the reverse is true, and the 10,000-foot level would be lower. The adjustment made by the pilot to compensate for nonstandard pressures does not compensate for nonstandard temperatures. Therefore, if terrain or obstacle clearance is a factor in the selection of a cruising altitude, particularly at higher altitudes, remember to anticipate that colder than standard temperature places the glider lower than the altimeter indicates. Therefore, a higher altitude should be used to provide adequate terrain clearance. A memory aid in applying the above is “from a high to a low or hot to cold, look out below.” [Figure 4-18] 

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