www.racekeeper.com -- very easy to install and setup in the car and on the laptop. Quite powerful analysis and comparison tools, segments, theoretical laps, speeds, braking points, 3-axis accelerometer, automatic GPS track map, heads-up real time display through an iPhone, ample data acquisition capabilities as well as plug-n-play OBD for rpm and throttle position.

According to an article Fahrenheit wrote in 1724,[4] he based his scale on two reference points of temperature.[5] The zero point is determined by placing the thermometer in brine: he used a mixture of ice, water, and ammonium chloride, a salt. This is a frigorific mixture which automatically stabilizes its temperature at 0 °F. (A mixture of ice and water also stabilizes, either freezing or melting at 32 °F though Fahrenheit did not use this point in defining his temperature scale). The second point, 100 degrees, was the level of the liquid in the thermometer when held in the mouth or under the armpit of his wife — subsequent refinements. Fahrenheit noted that, using this scale, water boils at about 212 degrees.[5]

Later, work by other scientists observed that water boils about 180 degrees higher than the freezing point and decided to redefine the degree slightly to make it exactly 180 degrees higher.[4] It is for this reason that normal human body temperature is 98.6 on the revised scale (whereas it was 100 on Fahrenheit's original scale).[6]

According to a letter Fahrenheit wrote to his friend Herman Boerhaave,[7] his scale was built on the work of Ole Rømer, whom he had met earlier. In Rømer’s scale, the two fixed reference points are that brine also freezes at 0 degrees and water boils at 60 degrees. He observed that, on this scale, water freezes at 7.5 degrees. Fahrenheit multiplied each value by four in order to eliminate fractions and increase the granularity of the scale (resulting in 30 and 240 degrees, respectively). He then re-calibrated his scale between the freezing point of water and normal human body temperature (which he observed to be 96 degrees); he adjusted the scale so that the melting point of ice would be 32 degrees, so that 64 intervals would separate the two, allowing him to mark degree lines on his instruments by simply bisecting the interval six times (since 64 is 2 to the sixth power).[8]