How is "engine lag" on Mt Gox calculated? When looking at external API-driven charts of Mt Gox trades, there is a "Trading engine lag" shown, which shows the backlog of orders queued and waiting-to-be-executed, relative to the present time:



(For example, see http://bitcoinity.org/markets, and http://bitcoin.clarkmoody.com/ )

How is the "engine lag" time calculated?
It is the difference between current timestamp and the submission timestamp of the oldest order submitted, which has not yet been processed by the order book.