Transposition
Transposition in MusiCAD means the number of semitones a part is played higher or lower than notated.
A double bass part is written using bass-clef but actually played an octave lower than its notation, so a transposition of -12 is needed.
A Bb-clarinet and tuba play the note Bb when reading C, so it needs transposition -2 to accommodate between reading and playing.
An alto-saxophone plays the note Eb when reading C, so it needs transposition +3 to accommodate between reading and playing.
A guitar can be used with a capo to play one or more semitones higher.
Transposition may be most easily accomplished using the part modification dialog with the button 
The transposition is shown in the score dialog and the part options dialog