Oil and Gas Operator: "Thiefing the tank” or “A thief in the night” (which one affects your oil sales?)

The tank thief and the plumb bob are two essential elements of the oil and gas operator’s toolkit. However, these two tools, when handled improperly, lead to foregone oil sales (and happy hauling & services companies…)
So, we’ve included two “Quick Tips” that some lease operators may have missed in Pumping 101…
Quick Tip #1:
When tagging the bottom of a tank with the thief, it’s important that the pumper takes great care not to lower the thief too quickly…
oil and gas operator
If the thief drops through the tank too fast, it can disrupt the balance between the oil and the tank “bottom”. Emulsions take time to settle. And once disturbed, a second (more accurate) reading may not be possible until several minutes have passed. Remember, any false readings may result in a deduction or price adjustment for an entire tank of oil.
Quick Tip #2:
When dropping the plumb bob into the tank, it should be slowed several inches before it touches bottom. Once the plumb bob touches bottom, it should be lifted approximately one inch and then dropped sharply.
oil and gas operaotr
Why just an inch? 
When the plumb bob hits bottom hard, it’s allowed to lean which marks the level of the tank’s bottom on a pumper’s gauge line at a higher level than the tank’s true gauge – up to 1/2 inch.
In a standard 200 barrel welded oil field tank, 1/2 of an inch is equivalent to .83 barrels of oil. Over time, a bottom that consistently reads .83 barrels higher than a tank’s true bottom can really add up over the life of a well…
We know it ain’t much, but it’s still good to know.
After all, it is your oil… 😛
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  • When I was taught the trade as a field gauger by Mobil Pipe Line the gauge line was required to drape over the index finger and the gauge line was lowered by that finger just until the bob made contact with the datum or the floor. Two consequative gauges were required. The “drop” method was hard to get the same gauge twice.
    Also check your and the oil buyers gauge line and plumb bob. I have seen bobs almost worn through the top and over 1/4″ off. Four tanks and you have lost a inch of oil.
    Another thing is the gravity temp and wood back temp. These should always be within 2 degrees F. If not either the gravity temp is not correct, the wood back is wrong or the gauger is jacking the temp.