Dropped A tuning

Dropped A tuning is an alternate tuning for a 7-string guitar where the lowest string is tuned down ("dropped") from the standard B by one whole step to A as follows A1-E2-A2-D3-G3-B3-E4. Also, for a 6-string guitar, dropped A tuning is achieved by tuning all strings down a 4th with the lowest string tuned 1 additional step down as follows A1-E2-A2-D3-F#3-B3. This is a "drop 1" tuning in the key of B (i.e. tune the whole guitar down a perfect fourth from standard tuning, then tune the 6th string a whole step down). As a result, it uses the same fingering as drop D tuning and drop C tuning.
An alternate dropped A tuning utilizes a guitar tuned to E Standard with the 6th string dropped to a low A, resulting in AADGBE with the 6th and 5th strings an octave apart.
Another variation of this tuning is AEADGB, which imitates a 7 on a six-string, excluding the high E.
Another dropped A tuning is AGCFAD ("drop perfect fourth in the key of the D", i.e. whole guitar is tuned down one step, then the lowest string is dropped to A).