As each estimate of position is relative to the previous one, errors are cumulative, or compounding, over time. These errors tend to compound themselves over greater distances, making dead reckoning a difficult method of navigation for longer journeys.įor example, if displacement is measured by the number of rotations of a wheel, any discrepancy between the actual and assumed traveled distance per rotation, due perhaps to slippage or surface irregularities, will be a source of error. Most notably, dead reckoning does not account for directional drift during travel through a fluid medium. For precise positional information, both speed and direction must be accurately known at all times during travel.

While dead reckoning can give the best available information on the present position with little math or analysis, it is subject to significant errors of approximation. The earlier value and the changes may be measured or calculated quantities. Often, this usage implies that the changes are not known accurately. īy analogy with their navigational use, the words dead reckoning are also used to mean the process of estimating the value of any variable quantity by using an earlier value and adding whatever changes have occurred in the meantime. Whether it is used to convey 'absolute' as in 'dead ahead,' reckoning using other objects that are 'dead in the water,' or using reckoning properly 'you’re dead if you don’t reckon right,' is not known. The original intention of 'dead' in the term is not clear however.

The term 'dead reckoning' was not originally used to abbreviate 'deduced reckoning,' nor is it a misspelling of the term 'ded reckoning.' The use of 'ded' or 'deduced reckoning' is not known to have appeared earlier than 1931, much later in history than 'dead reckoning' appearing as early as 1613 in the Oxford English Dictionary.

Computer air navigation dead reckoning