點可以知道1個bar 的調是什麼~~

要睇佢有無#同b
e.g. 有f # -> f 升上一個係 g,所以係g major
e.g. 有b同e b ->e b前一個係b b所以係b bmajor

點樣分別 Major key & minor key
first you collect all the flats and sharps
if you got a key-signature that fits all the b/# -----a major key

if you got a extra sharp , then take this extra sharp as the 7# of the minor
the 8th note is the tonic of the minor

if you got a missing flat, then take this missing flat's letter name as the 7# of the minor
the 8th note is the tonic of the minor

example:
if you got: C#, G#, D#, F#.... they all fit in E major, then the answer is E major
if you got: C#, G#, F# and E#...E# is the extra one....then F# minor is the answer
if you got: Bb, Gb, Db, Eb......A should have a flat but missing...then A-natural is the 7th sharp...answer : Bb minor