EC and PPM are easily converted. Here is a chart that shows how to go from EC to 500 scale and 700 scale or the other way around. EC is universal and is the best way to read and communicate nutrient strength. People say ppm and often don't know if they are reading on the 700 scale or the 500 scale. The 700 scale is a much higher reading than the 500 scale. 500 ppm on the 500 scale is the same strength as 700 ppm on the 700 scale. You can see how someone could be feeding what seems to be a high nutrient strength when in reality they are just measuring in a different scale.