The IMO requirement on Tanker Safety and Pollution Prevention, 1978 - Resolution A.446 (XI) 4.4.4. states "Means such as level gauges, hand dipping, and stripping system performance gauges as referred to in paragraph 4.4.8. shall be provided for checking that the bottoms of cargo tanks are dry after the Crude Oil Washing. Suitable Arrangements for hand dipping must be provided at the aftermost portion of a cargo tank and in three (3) other suitable locations unless other approved means are fitted for efficiently ascertaining that the bottom of every cargo tank is dry."

So the simplest method for checking dryness of tank bottom is to lower a Dipping Scale suspended from the graduated stainless steel tape constructed in the Reel Device to the tank bottom and read-out the level adhered remaining oil on the Dipping Scale.

Portable Tank Bottom Dryness Checking Device is constructed basically to be coupled with Tank Gauging Station (Vapor Locks) to permit releasing only minimized inert gas from tank in accordance with "CLOSED" requirement and GROUNDING of the device in order to avoid explosion due to accumulation of static electricity after tank washing.