ppm's are pretty simple concept to understand. ec/tds meters are the same thing basically. total desolved solids=parts per million in the solution. say 1 ts of nutes makes the water 500 ppm's...hell i dont know. haha. i just got one. i am guessing you use that meter to get a nute recipe down pack for a certain strain you grow or to stay in the ballpark range of ppm's during the differnt stages