When crude oil is moved by tanker, one way of diverting it is to pump off crude oil as 'slop oil,' which is then subtracted from the ship's cargo. This slop oil may have the same value as the original shipment and be sold for the profit of the ship's crew. Crude oil has also been diverted on a large scale by unloading the entire cargo in an unauthorized port and sinking the tanker, but this is generally an insurance fraud. Some oil is moved from port to port by using 'sport charter,' which are tankers that move looking for fares. These shipments are generally at greater risk because the controls are fewer and the possibility of redress becomes more remote because of international ramifications. In stealing oil from barges, some thieves have found ways to deceive the petroleum measurement inspectors, who drop a measuring tape through the crude oil to get the exact depth. Objects are sometimes put on the bottoms of the tanks to disguise the true depth of the oil on the barge. Also, meters, being mechanical devices, are subject to alteration to benefit either the buyer or the seller. The techniques involved depend on the type of meter, mode of installation, built-in protection, and other factors. Samplers are mechanisms which permit technicians to collect a given quantity of oil for analysis, which helps in determining the value of the shipment. These are also subject to manipulation. Diversion when crude oil is carried by tank truck can be largely controlled by limiting entry to the pipeline system and providing a tamper-resistant sampler at every point of entry. Refined petroleum products moved by pipeline may be diverted by tapping the pipeline, but this can be detected through meters that are routinely inspected.