What is the difference between imprest fund system and fluctuating system in Petty cash?

Imprest fund is a fixed cash or petty cash in the form of coin or other currency that has been advanced to the cashier while fluctuating fund system  is handling petty cash fund wherein expenditure, voucher/receipt is debited directly with petty cash fund as credit. 

Imprest Fund  system, "In this system the amount of petty cash funds in the account alwaysRemains, in the amount of the check is handed over to the cashier to petty cash to Establish a petty cash fund".

Fluctuation Fund System  ‘’In a system of petty cash account balance fluctuations fixed, but fluctuates According to the amount of back filling and expenditure-expenditure of petty cash".