Spells you cast cost {1} less to cast. You must speak in a voice other than your normal voice. When you speak in your normal voice, sacrifice this artifact.
Bronze Calendar has 2 printings, first in Unglued (1998). It has 2 official rulings.
Legality
commander: not legal
legacy: not legal
vintage: not legal
pauper: not legal
modern: not legal
pioneer: not legal
standard: not legal
brawl: not legal
Rulings
: You may change voices as often as you wish, as long as you avoid the one you use normally.
: If you control more than one Bronze Calendar, speaking in one voice that isn’t your normal voice will satisfy the requirements of all of them.