This is the Leica proprietary calculator, but it may end up being close or correct for you.
Plug in your load details. Set your unit of measurement. Set your zero range. Have it calculate.
Then go to the tab for their ballistic reticles. There is one similar to your Christmas tree. Plug in variables until you find a zoom distance that creates subtension ranges that seem somewhat easy for you to remember. (e.g. 150-200-250-325-etc)
You'll then have to go to the range and test at that zoom range to see if it works....it won't. You'll then fidget with your scope with slightly more or less zoom than it says on the dial and it will eventually work. Then you put a piece of tape on your scope and use a pen for a witness mark. For the rest of your days, you'll be constantly looking at that zoom dial making damn sure it didn't move whatsoever to a different magnification, otherwise your subtensions will all be off.

Leica - Ballistic Tool
https://ballistictool.leica-camera.com
Plug in your load details. Set your unit of measurement. Set your zero range. Have it calculate.
Then go to the tab for their ballistic reticles. There is one similar to your Christmas tree. Plug in variables until you find a zoom distance that creates subtension ranges that seem somewhat easy for you to remember. (e.g. 150-200-250-325-etc)
You'll then have to go to the range and test at that zoom range to see if it works....it won't. You'll then fidget with your scope with slightly more or less zoom than it says on the dial and it will eventually work. Then you put a piece of tape on your scope and use a pen for a witness mark. For the rest of your days, you'll be constantly looking at that zoom dial making damn sure it didn't move whatsoever to a different magnification, otherwise your subtensions will all be off.
Leica - Ballistic Tool
Leica - Ballistic Tool
https://ballistictool.leica-camera.com