The "fractional account value" for a base currency is the current worth of all funds managed by the bot restricted to the markets with that base currency.
It is calculated as follows:
The total amount of this base currency in the user wallet on the exchange, minus
any base currency that was acquired by the bot on "other" markets that coincidentally have this base currency as target currency, plus
the current worth of all acquired coin on the markets for this base currency.
Consider this example:
A user has 1 BTC, 10 ETH and 5000 ADA in their wallet and is trading on Binance:ETHBTC and Binance:ADAETH, where 4 ETH was acquired on Binance:ETHBTC.
Assuming the 5000 ADA is currenty worth 1 ETH, then the "fractional account value" for ETH is: 10 (in wallet) - 4 (from "other" markets) + 1 (current worth of ADA in ETH).
Note: For this value to be calculated properly, it is important to keep the "Accumulated Funds" in sync with the wallet on the exchange when trading manually or withdrawing funds that were acquired by the bot. See also the article on "Release reserved funds".