@Tbaac: The vertical line at the top (90 degrees), is the place where you set the observed mast height when looking with high power zoom. The lower one, at 14.5 degrees, is for observed height at low power zoom. Then you can read the range on the outside scale of the middle moving disk, opposite to the target'srecognition manual mast-height.
The line of pins in between is to read the speed in knots, after the time of passage through periscope/UZO line is aligned to ships length. (length is outermost scale, time in seconds is on adjacent scale.) You have to be stopped to use it, OR only moving forward or backwards.
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