Once the location for A2 is known, mapping A1 is very straightforward.

A good location for A1 is as a 6:3 octave (from A2), 3.0 cents wide.

Here’s how to do that with a SAT:
1.  In TUNE mode, set the SAT to (E4 @ x.x), play A2 and stop the lights using the cents buttons.
2.  Look at the cents setting in the SAT display
3.  Subtract 3.0 c. from that cents number and then tune A1 to that setting.
Now A1 has been tuned as a 3 c. wide 6:3 from A2.

For example: If the cents setting in the SAT display after doing both step 1 and 2 above is (E4 @ 1.0), subtracting 3 c. from that number would be give us a SAT setting of (E4 @ -2.0).

[Write this 6th Partial number (-2.0 c.) down, because it will be used later to map A0.   So, for mapping A1 you will need to write down 2 numbers:
1. the 6th P location and
2. the 4th P location].

Tuning A1 to (E4 @ -2.0) gives us a 3.0 c. wide A1/A2 6:3 octave.

Give it a listen and tweak as you see fit.   But if the mapping of the prime and the sub prime is fairly well done, this 3.0 c. wide A1/A2 6:3 will work 99.9 % of the time.

If you have some other way you prefer to find the location for A1, that’s fine.

Tune it however you want, but when you’ve found the best location for A1, you must measure A1’s location using its 4th partial.

The LC spreadsheet uses the 4th partials from A0 – A4.   Even though A1 is tuned using it’s 6th partial, that tuning location needs to be measured using it’s 4th partial so the LC spreadsheet can use A1’s location.

Be sure to write down the 4th Partial location of A1 so it can be entered into the LC spreadsheet for creating the tuning.