Abacus

You draw a small, harmless, immovable, and intangible numeral in the air, of any color or opacity you choose. While writing this number, you can choose a triggering effect that will modify the numerical value using addition, subtraction, multiplication, or division. Every time the effect occurs within the spell's range, the written numeral is modified by a value you set as the spell is cast.

The number can never be larger in size than the area of the spell's effect. If the length of the value exceeds what the area would allow, the graphical size of the number shrinks to include the full value inside.

Anyone within the spell's range can dispel it or reset the value with an Action if they are aware the Abacus is present.