I'm training my voice and need a point of reference.
On guitar, you can use an open string. Start open ("0"), and use the following pattern:
0 2 4 5 7 9 11 12
The open strings are, from heaviest to lightest, E A D G B E.
You can just add to the above pattern if you want to start on a different fret. For instance, if you want to use the F# major scale, start on the E string, 2nd fret, and use: 2 4 6 7 9 11 13 14
If you meant something different in your question, please clarify. :)