Matched Volume Multiple Markets

[Ztown]

What is the best way to get the matched volume on multiple markets?
For example, let's say I want to get the matched volume for 10 marketid's? What is the best way to do this?

[AlgoTrader]

Switching to a NG API and using a single listMarketBook call

[Ztown]

What does "NG" stand for? The new api?

[Ztown]

How hard is it to migrate to new API? I am using C++.