I've briefly tested my 'virtual' omnimeter by comparing my TDC data with what the omnimeter shows.
Allowing for the discrepancies caused by the fuzzy graduations on the virtual omnimeter it actually seems to work!
Here's what I tried;
1. Get mast height from ID book then slide this figure on the omnimeter. (pause game, alt-tab to my virtual omnimeter slide rule on desktop etc).
2. Get range to target using TDC and stadimeter.
3. Check scope graduation indicated on omnimeter by the combination of the mast height and range data.
4. Check on periscope (high power) to see if marks on periscope match what omnimeter tells me (i.e. omnimeter indicates 2 1/2 graduations on high power on the scope should match the mast height in my scope picture). It seems to work better if the scope marks are set from the main deck to the mast top as opposed to from the surface of the water to the mast top.
It seems to work albeit not exact. I've only used high power markings so far as low power doesn't give a good clear indication of the masts at distance (at least on my poor rig).
I haven't figured out what the angle on the bow slide is supposed to do as yet.