Back in those times, nobody had the experience or practice to make the things they painted look realistic. They didn’t really have the years of experience of people before them to go off of. Also, they probably had quite limited tools.
It's okay if you don't know
Example: Transposing from a C instrument to a B-flat instrument.
Move the key up one whole step (or whole tone).
Our key of C Major transposes to a key of D Major. Likewise, G Major would transpose to A Major, B-flat Major to C Major, and so on.
Sory