The C6 TUNING SLIDE RULE CHART FOR 8 STRING STEEL GUITAR is an 8.5"x 11" laminated chart showing every note in every key over the neck.  The tuning is A-C-E-G-A-C-E-G.  For instance, above each fretboard are 4 related keys.  The area on the end are the open strings.  If the first chord of a song is C Major, like the chords: C Am F and G, improvise using C Major fretboard or C Major/m7 fretboard.  Usually, the first chord indicates the key.  If the chords of a song begin in Em, use the fretboard for E minor or E minor/Maj6.  Every note showing would be in that key along with your improvised leads or fill in riffs. Try it!