[sciurius]

Hi Skip, thank you for chiming in.

In the world of lead sheets and ChordPro files, we use the enharmonic model, where D# is equal to Eb and so on. Most guitar players will pick whatever comes out handy. For example, I personally prefer Bb over A# while I also prefer C# over Db.

More formally, a piece of music has a key which determines the tonality of the piece. In sheet music, the key is denoted by the signature (see, e.g. https://en.wikipedia.org/wiki/Key_signature). The number of flats/sharps determine the key. C has no sharps nor flats, G has a single sharp (F#), D has two sharps (F# and C#), A has three sharps (F#, C# and G#) -- see a pattern?
Likewise, F has one flat (Bb), Bb has two flats (Bb and Eb), Eb has three flats (Bb, Eb and Ab), and so on. The two series meet at Gb (six flats) and F# (six sharps), both being enharmonically equivalent.

There are two things to note here. First, a key signature only has flats, or sharps, but not both. Second, there's no signature for minor keys, they are considered the same as their major partner (Am -> C, Dm -> F, etc.).

When transposing a piece of music we change its key, for example from G to A. Since A has three sharps, we expect the chords (from G) E, B and F to become F#, C# and G# respectively.

But what about going down, from G to F? E and B become D and A, no problem. F becomes D#? or Eb? The convention is that since key F has one flat, we must use flats for the other chords as well, so chord F becomes a Eb.

The remaining problem is when the destination key is C, with no flats and sharps. For example, going from key A to key C, the F chord could become G# or Ab. AFAIK there's no convention for that.

Referring to the two sites you mention: http://www.guitar-chords.org.uk/chords-k...minor.html deals with chord progressions and has nothing to do with transpositions.

http://www.transposechords.com/how-to-transpose-chords is very lax and informal (i.e., the average guitar player ). It uses sharps and flats at will, for example, C C# D Eb F ... Also, it sharps E into E# (instead of F) but sharps B into C.