Weight on bit Weight on bit Weight on bit (WOB), as expressed in the oil industry, is the amount of downward force exerted on the drill bit and is normally measured in thousands of pounds. Weight on bit is provided by drill collars, which are thick-walled tubular pieces machined from solid bars of steel, usually plain carbon steel but sometimes of nonmagnetic nickel-copper alloy or other nonmagnetic premium alloys. Gravity acts on the large mass of the collars to provide the downward force needed for the bits to efficiently break rock. To accurately control the amount of force applied to the bit, the
Standard atomic weight billion for the others. However the range of natural abundance for the isotopes is such that the standard abundance can only be given to about ±0.001% (see table). The calculation is The estimation of the uncertainty is complicated, especially as the sample distribution is not necessarily symmetrical: the IUPAC standard relative atomic masses are quoted with estimated symmetrical uncertainties, and the value for silicon is 28.0855(3). The relative standard uncertainty in this value is 1 or 10 ppm. To further reflect this natural variability, in 2010, IUPAC made the decision to list the relative atomic masses of 10 elements as