Battenberg course indicator The Battenberg course indicator is a mechanical calculating device invented by Prince Louis of Battenberg in 1892 for taking station on other vessels whose range & bearing and course & speed are known . By extension , it has a range of other functions related to relative velocity calculations . A number of versions of the device were produced and it proved particularly useful for station keeping , such as ships moving in convoy during World War II . Manufacture of the instruments was contracted to Elliott Brothers , London . Devices based on the Battenberg indicator were also developed for determining course and distance in aviation and when making allowances for aircraft drift due to winds . Instruments were also manufactured for other navies , for example in the USA . Mark I . Prince Louis of Battenberg employed a firm of London instrument makers to build a prototype to his design . The device comprised : To use the instrument , the course of the flagship was first set on the guide bar . When the initial and final stations had been set using the position bars , the speed ratio clamp was set to show the ratio of own ship speed to the speed of the flagship ( if the flagship was doing 10 knots , and the manoeuvring ship had 15 knots available , the clamp would be set to " 1 . 5 " ) . Ensuring that the pin beneath the speed ratio clamp was set within the diameter grove , the course required to take station could then be read off the circular disc . Mark II . The Mark II version dispensed with the use of relative speeds and set the guide bar on a sliding speed scale , thus allowing the speed of the guide and the speed of the own ship to be set independently . The device was constructed largely of brass . Mark III . The Mark III instrument was constructed of aluminium alloy . Mark IV . Similar to Mark III . The circular scale attached to the end of the ' own ship ' bar was moved to be part of the pivot assembly , so that it is fixed relative to the ' guide bar ' instead of being fixed relative to the ' own ship ' bar . The ' own ship ' bar was redesigned with a pointer on the end to read off the scale . Mark V . The mark V instrument dispensed with the guide bar and own ship ' s bar , retaining only the two position bars . However the circular base plate was added to by the provision of two celluloid transparent discs which were placed on top of the base and free to rotate . The instrument body was made in an aluminium alloy , and had a scale graded in degrees around the outside . The base plate had no scale , but a series of interrupted parallel lines running across it . This device was in production around 1955 . One disc was marked with a scale from 0 at the centre to 36 on the outside , in a similar manner to the markings originally etched onto the base plate , except that three marked scales were used , one in a line through the centre and another parallel but half way to the edge either side of the centre line . The markings were then repeated by a second set at right angles to the first . Depending on usage , the marked scale numbers could refer to distance or speed . A second disc was marked with a circular scale all around the edge labelled in degrees , with radial lines from the centre of the disc stretching out every ten degrees . The disc also had concentric circles which coincided with the marked scale on the other disc . To aid clarity , markings on the second disc were in a different colour to those on the first . The rear of the device had a separate rotating calculator , where if the ships speed was set against the 60 - minute guide mark , then the distance travelled in any time 0 – 60 minutes could be read off against the logarithmic time scale .