I think about this every so often. I thought I'd throw it out there this time.
I was hired to be the "German accordionist" with a band last year. I never played with them before. I did the customary "salute" during playing to advise the band members what key I was going into. Every time we ended up playing in different keys.
I questioned the guitarist. I said I had one finger "UP" meaning I'm going into the key of G. Two fingers "DOWN" means entering B flat. He argued endlessly that I had it wrong...one finger up means F and two down means D.
I haven't played in a band in years. Do I have it wrong?
Mark,if your original key was C in your example, you are using circle of fifths (accordion players)...
If your guitar guy was in the key of E...than he is correct..
I have always based on half steps.up or down, self explaining. Up 1, raise a half step..
Even girl singers get this.