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# External Custody

## **Overview**

DUET adopts a money market protocol as "external custodian" to carry out the following functionalities: 

* Holds and secures user capital in one or several base tokens; 
* Calculates a total dynamic effective value of the user capital deposited.

## AAVE: The Money Market Protocol on Abitrum

For the trading business to better scale, DUET Protocol adopts AAVE as the external custodian on Abitrum. AAVE does not just hold capital but also calculates its dynamic effective value. 

The support of multiple base tokens is more systematical, as users can choose to deposit any token supported by AAVE, e.g. USDC, DAI, WBTC, ETH, LINK.

When users deposit several kinds of tokens, the real-time total dynamic effective value of the tokens is calculated by AAVE with some built-in functions.


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