Never subscribed myself but have been aware of it for decades and still employ the theory which is quite simple and logical.
In a nutshell: Open Interest, volume and price are the tools.
Open interest- since opening a futures contract requires the margin $$ the total # of contracts gives us the amount of $$ coming into or going out of that futures mkt.
Price- price reveals the direction that $$ is pushing the mkt.
Volume- represents velocity of price change.
Duh, how else would it be? They are neutral when their system can't get a read that turns them on.
Open interest is published early in the a.m. for the previous day. It can be very revealing. If there's a big up day and the next a.m. your system shows considerably less O.I. you know they closed their longs and not to expect much more to the upside. If there follows a large vol day without much price movement and the next a.m. O.I. is way up you know they opened shorts into the retail buying because vol was up but not price, no velocity to vol at the turns.
Of course we never know for sure but sometimes I pretend I do, I have to trust somebody.