With your pen set to EC, take a reading. What does it say?
Then change the mode to PPM. If need be take another reading. What does it say?
you will be able see what scale is being used
EC of 3 x 700 -=2100
All I am saying is if you pen reads in 500 scale it will show ppm of 1500. If you think, to get the proper nutrient mix you need to add more nutrients to get it up 2100, it would be a mistake. You would be over fertilizing.