The user's underlying balance, representing their assets in the protocol, is equal to the user's oToken balance multiplied by the Exchange Rate.
OErc20 / OEther
function balanceOfUnderlying(address account) returns (uint)
account: The account to get the underlying balance of.
RETURN: The amount of underlying currently owned by the account.
OErc20 oToken = OToken(0x3FDA...);
uint tokens = oToken.balanceOfUnderlying(msg.caller);
const oToken = OEther.at(0x3FDB...);
const tokens = await oToken.methods.balanceOfUnderlying(account).call();