TM 1-1500-204-23-4 Figure 4-17.  Dual Synchronous Rotor Tachometer Wiring Diagram (Grounded Two-Wire System) (2) Testing. The following paragraphs describe   tests   and   replacement   criteria   for   electrical resistance temperature indicators. (a) Continuity  check  test.    Test  wiring for  proper  continuity  as  specified  in  applicable  wiring diagrams. (b) Master   thermometer   test.      Master thermometer  test  Using  an  electric  thermometer  tester, test indicator for proper operation. (c) Bulb     test. Using a precision ohmmeter or a Wheatstone bridge, test bulbs for proper resistance values. (d) Replacement criteria. Replace indicators   or   bulbs   when   proven   faulty.      Repairs   of damaged wiring shall be per Section VII of TM 55-1500- 323-25. I. Thermocouple Temperature Indicators. Principles   of   operation   and   testing   of   thermocouple temperature   indicators   are   described   in   the   following paragraphs. (1) Principles of operation.  The thermocouple temperature indicator consists of an indicator, bulb, and connecting leads. (2) Testing. The following paragraphs describe tests and replacement criteria for thermocouple temperature indicators. (a) Resistance  test.    Disconnect  leads from indicator and test for proper lead resistance with a precision ohmmeter or a Wheatstone bridge. Resistance  value  must  be  as  specified  on  back  side  of indicator.    Repair  or  replace  leads  when  resistance  is other than specified. (b) Master thermometer test.    With  on- lead   disconnected,   indicator   must   read   within   18° F (10° C)  of  surrounding  temperature  when  tested  against a   master   mercury   thermometer.      Indicator   may   be adjusted  to  read  tolerance  with  zero  adjustment  screw. When indicator cannot be adjusted, it must be replaced. m. Outside Air Temperature Gauges.  Principles of operation and testing of outside air temperature gauges, as   shown   figure   4-18,   are   described   in   the   following paragraphs. (1) Principles    of    operation.        Outside    air temperature gauges show outside air temperature.  The system usually consists of an indicator, bulb, and circuit breaker. (2) Testing. The following paragraphs describe the test procedures and replacement criteria for outside air temperature gauges. (a) Master    thermometer    test.        Test outside   air   temperature   gauges   using   the   following procedures: Figure 4-18 Outside Air Temperature Gauge 4-23