Notation Question
 

What does a number inside a square mean? It goes in order of 1, 2, 5, 6.

Most likely it indicates a harmonic. Symbols in different tab programs can vary somewhat.

What kind of notation system? Can you post an image? I can think of at least two different interpretations (one for standard notation, one for Nashville Number System notation). And both of my guesses could be wrong, it could be something else...

In standard notation, a number inside a box could be used as a measure marker or rehearsal marker. “Let’s start it again at section 2.” Might also be denoted as a circle instead of a box, and / or, a letter instead of a number. This kind of rehearsal marker is often used in choral and band arranagements (situations where there is an an ensemble playing and behing rehearsed by a conductor).

In Nashville Number System, if there are two chords in a measure, it’s common to see them with a box around them (so you know it’s a single measure). For example a common turnaround progrsesion would be, in jazz lead sheet chord symbols:

iii vi | ii V | I

In NNS you might see, for the same progression:

[3m 6m] [2m 5] 1 (with the brackets being a box in the hand written version)

Its a blues tune for guitar, the squared number is located between the standard notation and the tab. I would post a picture but its a PITA on this site, hoping the description is enough.

Well you’ve stumped this chump. I can’t say I know the answer. I spent five minutes flipping through my stack of method and song books and could not find anything that seemed like what you describe. I did see notation for harmonics but that was more of a diamond, and it was on the tab lines, not between the tab and staff.

My last guess would be that somehow the arranger is trying to signal what string to play a note on? But you said it’s both standard notation + tab so that seems redundant...

If you can email me the picture I can post it for you. I pm'd my email address.

I replied to your pm

Here is what Merak is referring to
 

My apologies for the delay Merak!

https://i.imgur.com/Uwoyek7.png

Is it the bar number relating to notes elsewhere?

This is just a guess:
It might be the transcriber's way of splitting the tune into parts or chunks that are similar. For learning purposes.
I've seen it done in other music, but usually with letters instead of numbers.

But only a small snippet was provided in the pic, so I'm not sure if this guess makes sense.
I don't think it's a very common practice in any case.

That's my guess, as well. It looks like they refer to sections of the composition.

Now seeing the notation example, am agreeing it looks like a rehearsal mark.

Thanks for looking at it, and to Cecil for posting the picture for me, many thanks. Just wanted to make sure I wasn't missing a detail on how the piece is to be played.