![dapp-a-day-24 2x](https://cloud.githubusercontent.com/assets/6280810/18398049/31d2f5fe-76cb-11e6-9947-049991c11abd.png)

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A `Rate Accumulator` is a building block for tracking a set of balances with a continuous variable return rate. It will correctly prorate balances in constant time no matter how frequently the rate is updated or balances are changed *(each at most once per timestamp)*. 

This comes at a cost of storage space that is linear with number of *"points"*: Any time the rate is changed or a balance is read, a storage slot is polluted forever. Reuse rate accumulators whenever possible - the same accumulator can be used for totally different balance sets with no extra penalty.

### https://github.com/nexusdev/ds-rate-accumulator