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.
Read more about this topic: Battenberg Course Indicator
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