Devil's Abacus is a passive item in Fiend Folio, a mod for The Binding of Isaac.

Firing X tears at once and then stopping will grant a small damage and fire rate increase, with the stat boost increasing with each successful count.

The amount of tears that need to be fired at once in order to accomplish this increases by +1 each cycle, starting at 1, then 2, 3, 4, etc., hence the item telling you to count.

Stat boosts are equal to log(1 + TearsFired / 3).

Counting is valid as long as one fire button is held. Shooting direction can be changed by obeying this rule.

A successful count will be represented by the count number appearing over Isaac's head when a shooting cycle is finished, and a musical instrument playing. Failing the count will reset the tears required to 1, reset the stat boost, and play a fail sound.

There is no limit on the tear counter, hence the stat boosts. The fire rate granted can break the default cap.

Devil's Abacus can be found in the following item pools:

The following tags are applied to this item:

• Check out the item description on the mod's external Wiki.
• Download Fiend Folio from the Steam Workshop.