I've been trying for a long time to get the notepad working in the UZO, Attack, and Obs scopes. Well tonight I finally figured out how to do it

Now you have a working stadimeter
I'll detail the process of how to use it now:
in this screenshot I measured the distance from my sub to the target - range was 8100m
next thing I do is open up the XO TDC dialog box and turn TDC on (if you don't then when you open the notepad you'll get the exact range to the target - spoiler!)
now I click on the autohide button of the notepad causing it to slideout. Since the messagebox covers it I hide the messagebox by pressing the L key
I use the XO TDC dialog box to identify the target ship. Notice the information in the notepad
now I click on the range button on the notepad
which brings me back to a familiar page from SH3....time to use the stadimeter to get range! Notice the information in the notepad. Mouse cursor is on the crosshairs ready to click it (activate stadimeter)
got my double prism now I'm lining it up with the highest mast on the ship
I think it was aligned correctly so I click the mouse button and to my surprise range is reported as 8205m!!

The range TDC dial even indicates correct range.
angle on bow and speed of the notepad also work just like they did in SH3
You'll see this in the next version of the UIs mod