Each custom token you add to the BC Vault requires you to also enter decimal places. BC Vault will try to automatically parse that information from the blockchain if available (from v1.7.0).
It is also possible to manually change that definition. Should a discrepancy between the entered information in the application and available information from the network/blockchain occur, the device itself will let you know about that.
This is important, since if you use wrong multiplier you will see wrong numbers in the application. You might for example see 10 tokens, where you have 1000 (or vice versa). This would also mean that when sending, you would try to send 10 tokens from the application, but in reality, you would send 1000 tokens.
Example for Tether (TUSD) on Ethereum:
Correct decimal places:
TUSD decimal places: 6 Displayed value: 10,00 USDT
Wrong decimal places:
TUSD decimal places: 4 Displayed value: 1.000,00 USDT
Such mistakes are caught on the device and following warning will be displayed:
"Decimals setting for this custom token differs from the blockchain."
We recommend, you cancel the transaction and carefully recheck your custom token definition as per: Custom ERC20 Tokens