A unit of counting rate used for scaling [[gamma-ray log|gamma-ray logs]] and [[neutron log|neutron logs]]. (1) For gamma-ray [[curve|curves]]. The difference in curve [[deflection]] between zones of low and high radiation in the [[API]] gamma-ray [[calibration]] pit is 200 API gamma-ray units. One two-hundredth of this deflection is one API gamma-ray unit. (2) For neutron curves. The difference between [[electrical zero]] and the curve deflection opposite a zone of Indiana limestone (19% [[porosity]]) in the API neutron calibration pit is 1,000 API units. One one-thousandth of this deflection is one API neutron unit.