TM 10-3930-664-10 2-4. MISCELLANEOUS CONTROLS AND INDICATORS. a. Hydraulic Filter. KEY OR CONTROL FUNCTION 1 Clogged Filter Indicator Indicates  when  hydraulic  filter  needs  servicing.    Indicator  gradually  moves from GREEN zone to RED zone as contaminants removed from the oil clog the filter. b. Hydraulic Tank. KEY OR CONTROL FUNCTION 1 Sight Gauge Indicates the level of hydraulic oil in the tank.  Oil must be between the LOW and HIGH marks on the gauge with the mast lowered to ground level and the engine not running. 2-12

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