When you promote a Character or a Maker or hit a maker quota bonus, you will gain a multiplier that will help with your farm.
There are three types of multipliers:
Cash - increase the base profit of a specific Maker or all Maker
Speed - decrease the time needed to make a dairy product
Milk tapping power - increase tapping power when you do Milk tap challenge!
Most multipliers are for Cash, and cash multipliers will only apply to the base amount that the Maker earns. So if your previous multiplier for the Maker was x2 and your new multiplier is x20, the x20 replaces the x2 and you earn base amount x20, not base amount x40. Combined with multipliers from other character additively
Example: For cards upgrade, if you earn 1 per cycle, and gain a x10 Cash multiplier, you now earn 10 per cycle. If you gain a x25 Cash multiplier, you now earn 25 per cycle, as the x25 is for the base amount and replaces the previous multiplier.