Another thing those horizontal degree marks on your periscope can do is judge distance if a ship is at a 90 degree angle on the bow to you. You can also visually fudge this.
Work in progress, I will have this done soon. This chart a copy of a German one used in wartime, cleaned up a bit so I can understand it. Hectometers! Seriously. I think they just did this so the numbers would fit on the chart.
Add a zero at the end of everything...
