TM5-4220-231-14&P Table  2-1.   Operator   Preventive  Maintenance  Checks   and   Services   For  DivingOperations   -  (Con't). B-Before D-During A-After W-Weekly ITEM INTERVAL ITEM   TO   BE    INSPECTED. Equipment is NO Not   Ready/ B D A W PROCEDURE Available If: 4 0 0 Valves (4). Check all valve   control knobs for Valve knob is operability. Turn   each knob counterclockwise to missing, the   open position and    then clockwise to   the broken or closed position. Replace control knob if missing valve or   broken. operation is jammed, excessively tight, or loose. WARNING Extreme care must be   exercised when handling pressure gages. Failure    to   keep gages free    of  oil, grease, rust,    or   contaminants may cause damage or   inaccurate readings. Failure    to   observe this warning may result in  equipment failure, injury,    or death to   personnel. 5 0 0 Gages (5). Inspect for  damaged pointers, Lens is cracked or   broken lens, missing or  unseated missing or retaining ring,   or  other visible    damage. Replace if broken. damaged. Needle pointer is damaged or not   adjusted to   0   psig. 0 0 Ensure pointer is  set    to   0  psig. Adjust as required. 0 Monitor gages to   ensure proper pressure ranges Sudden drop during operation. in  pressure affects diver's breathing (EXECUTE EMERGENCY PROCE- DURES, para 2-10). 0 Check depth gages for  accurate readings. Depth gage shows inaccurate reading. 2-18