Open Tunings: The Joni Mitchell Method

Take the example of standard tuning - i.e E A D G B E
You start with some standard pitch reference (a guitar tuner, tuning fork etc) to give you the note for the lowest string - E.
Depress the E string at the 5th fret to give you the note for the next string (A).
Then you fret the A string at the 5th fret to tune the next string (D) and so on.
Writing normal tuning this way would be : E 5 5 5 4 5
Which means:
E: Tune your lowest (6th) string to E (using a tuning fork, piano, or other reference)
5: Fret the 6th string at the 5th fret, and tune your 5th string to this note.
5: Fret your 5th string at the 5th fret and tune the 4th string to this note.
5: Fret your 4th string at the 5th fret and tune the 3rd string to this note.
4: Fret your 3rd string at the 4th fret and tune the 2nd string to this note.
5: Fret your 5th string at the 5th fret and tune the 1st string to this note.
[Note: the lowest string is called 6, the highest is called 1.]
Note that you only need one note name and five numbers to specify each tuning.
This system makes comparisons between different tunings easier. For example, the connection between a tuning of C# F# B E G# C# and standard tuning isn't obvious at first glance.Writing the two in the 'Joni' system, the connection becomes clear :
Tuning 1 : C# 5 5 5 4 5
Tuning 2 : E 5 5 5 4 5
In other words, the relative tuning of the strings is the same, it's just the starting note that differs.