are to be used and allowed to come up to temperature least 2 hours prior to use. Scales should not be used in  temperature extremes below 40 °F or above 100 °F unless the  scale is specifically designed for use in those temperatures.  Electronic scales are very sensitive and, if subjected to  freezing temperatures, the liquid displays may be damaged  beyond use. the aircraft is in level-flight attitude. Any fuel remaining in  the system is considered residual or unusable fuel and is part  of the aircraft empty weight. The amount of residual fuel and its arm are normally found  in Note 1 in the section of the Type Certificate Data Sheets  (TCDS), “Data pertaining to all Models.” For additional fuel  capacity information, see Chapter 2, Weight and Balance  Theory. If it is not feasible to drain the fuel, the tanks can be topped  off to be sure of the quantity they contain and the aircraft  weighed with full fuel. After weighing is complete, the  weight of the fuel and its moment are subtracted from those  of the aircraft as weighed. To correct the empty weight for  the residual fuel, add its weight and moment. The aircraft should be weighed inside a hangar where wind  cannot blow over the surface and cause fluctuating or false  scale readings. The aircraft should be clean inside and out,  with special attention paid to the bilge area to ensure that no  water or debris is trapped there. The outside of the aircraft  should be as free as possible of all mud and dirt. All of the required equipment must be properly installed, and  there should be no equipment installed that is not included in  the equipment list. If such equipment is installed, the weight  and balance record must be corrected to indicate it. When computing the weight of the fuel (e.g., a tank full of  jet fuel), measure its specific gravity (sg) with a hydrometer  and multiply it by 8.345 (the nominal weight of 1 gallon of  pure water whose sg is 1.0). If the ambient temperature is  high and the jet fuel in the tank is hot enough for its specific gravity to reach 0.81 rather than its nominal sg of 0.82, the  fuel actually weighs 6.76 pounds per gallon rather than its  normal weight of 6.84 pounds per gallon. All required permanent ballasts must be properly secured in  place. All temporary ballasts must be removed. Standard weights are established weights for numerous items  involved in weight and balance computations. These weights  should not be used if actual weights are available. Some of  the standard weights are listed in  Figure 3-4 . The empty weight for aircraft certificated under the Civilian  Air Regulations (CAR) part 3 does not include the engine  lubricating oil. The oil must either be drained before the  aircraft is weighed, or its weight must be subtracted from  the scale readings to determine the empty weight. To weigh  an aircraft that does not include the engine lubricating oil  as part of the empty weight, place it in level flight attitude,  then open the drain valves and allow the oil to drain out.  Any remaining is undrainable oil and is part of the empty  weight. Aircraft certificated under Title 14 of the Code of  Federal Regulations (14 CFR) parts 23 and 25 include full  oil as part of the empty weight. If it is impractical to drain the  oil, the reservoir can be filled to the specified level and the  weight of the oil computed at 7.5 pounds per gallon. Then,  its weight and moment are subtracted from the weight and  moment of the aircraft as weighed. The amount and arm of  the undrainable oil are found in Note 1 of the TCDS, and  this must be added to the empty weight. The hydraulic fluid reservoir and all other reservoirs  containing fluids required for normal operation of the aircraft  should be full. Fluids not considered to be part of the empty  weight of the aircraft are potable (drinkable) water, lavatory  precharge water, and water for injection into the engines. Note the difference in weight as  temperatures change.  Although this change is a very small amount per gallon, it could  end up in a significant total weight gain when dealing with large  quantities of fluids, such as those found in commercial aircraft. Drain fuel from the tanks in the manner specified by the  aircraft manufacturer. If there are no specific instructions,  drain the fuel until the fuel quantity gauges read empty when  3-4 Other Fluids Draining the Fuel Figure 3-4.  Standard fuels and weights with temperatures of 32 °F  and 59 °F. Standard Weights Ballast Equipment List Oil Weigh Clean Aircraft Inside Hangar Weighing Point AVGAS (Aviation Gasoline) JET A & A-1 Water Oil 6.14 6.75 8.35 7.50 6.01 6.68 8.33 7.43 Pounds per U.S. Gallon 32 °F 59 °F