TM 1-1500-204-23-4 1 Remove gauge to be shop tested. 2 Obtain mercury centigrade thermometer NSN 6685-00-851-4577. 3 Fill  container  with  fresh  water  and allow water to stabilize at room temperature.  (Allow to sit overnight, if possible. 4 Remove   sun   shields   and   suspend gauge in such a way that the stems are vertical and are immersed  two  to  two  and  a  half  inches  into  the  water. Simultaneously,  suspend  the  mercury  thermometer  in the water to an equal depth. 5 Record   the   mercury   thermometer and  gauge  temperature  after  five  minutes.    Allow  an additional five minutes to pass and record temperatures again.  Repeat until temperatures stabilize. 6 Fill   a   container   with   ice   cubes   or crushed ice and water. 7 Place the gauge with stems vertical into  the  ice-water  approximately  two  to  two  and  a  half inches. Simultaneously, immerse the mercury thermometer to the same depth. 8 Record   the   mercury   thermometer and  gauge  temperature  after  five  minutes.    Allow  an additional five minutes to pass and record temperatures again.  Repeat until temperatures stabilize. (b) Replacement criteria.  Gauges must agree with the mercury thermometer within two degrees at  both  test  points.    Failure  to  meet  either  test  point within two degrees is cause for rejection. (3) Temperature    Conversion.        To    convert Fahrenheit  to  centigrade  or  centigrade  to  Fahrenheit, use table 4-13 or the following conversion formulas. C = (5/9) x (F-32) F = [(9/5) x C] + 32 Example:  change 86 °F Example:  change 40C to Centigrade to Fahrenheit C = (5/9) x (F-32) F = [(9/5 x C] + 32 C = .5556 x (86-32) F = (1. 8 x 40) + 32 C = .5556 x (54) F = 72 + 32 C = 300 F = 104 n. Deleted. o. Magnetic  Compass.    The  magnetic  compass,  as shown    in    figure    4-19,    consists    of    liquid-filled    bowl containing a pivoted float element to which one or more bar  magnets,  called  needles,  are  fastened.    The  liquid dampens the oscillations of the float and decreases the friction of the pivot.  A diaphragm and a vent provide for expansion  and  contraction  of  the  liquid  as  altitude  and temperature  change.    Principles  of  operation,  compass errors, compass compensation, and replacement criteria are described by the following paragraphs. Table 4-13.  Fahrenheit-Centigrade Conversion Chart °C °F °C °F °C °F °C °F °C °F -50 -58 -20 -4.0 10 50.0 40 104.0 70 158.0 -48 -54.4 -18 -0.4 12 53.6 42 107.6 72 161.6 -46 -50.8 -16 3.2 14 57.2 44 111.2 74 165.2 -44 -47.2 -14 6.8 16 60.8 46 114.8 76 168.8 -42 -43.6 -12 10.4 18 64.4 48 118.4 78 172.4 -40 -40.0 -10 14.0 20 68.0 50 122.0 80 176.0 -38 -36.4 -8 17.6 22 71.6 52 125.6 82 179.6 -36 -32.8 -6 21.2 24 75.2 54 129.2 84 183.2 -34 -29.2 -4 24.8 26 78.8 56 132.8 86 186.8 -32 -25.6 -2 28.4 28 82.4 58 136.4 88 190.4 -30 -22.0 0 32.0 30 86.0 60 140.0 90 194.0 -28 -18.4 2 35.6 32 89.6 62 143.6 92 197.6 -26 -14.8 4 39.2 34 93.2 64 147.2 94 201.2 -24 -11.2 6 42.8 36 96.8 66 150.8 96 204.8 -22 -7.6 8 46.4 38 100.4 68 154.4 98 208.4 100 212.0 Change 3  4-24