What do Tapaas Volume and Market Value (exposure) figures display?

Tapaas takes the number of lots per trade and information as to how many units are in a lot, for each instrument, directly from the Trading Platforms.

Volume figures display the volume in units and these are further used for calculating the Market Value USD (Exposure). 

Market Value USD is the Net Open Position in units, which is revalued with the ask price if the Broker is long, or with bid price if the broker is short and convert it to USD from term currency.