[1] The basic characteristic of an imprest system is that a fixed amount is reserved, which after a certain period or when circumstances require, because money was spent, will be replenished.
The system operates on the principle of replenishment, whereby the petty cash fund is maintained at a constant level by reimbursing only the amount spent.
In an imprest system the amount requested is documented with petty cash dockets and their associated receipts or invoices.
In a petty cash system, receipts are written for each amount issued.
Any shortfalls may be addressed by the individual responsible for the float, typically a bookkeeper, using their own resources.