To add confusion, the truncheon has both scales, 500ppm=1 EC and also 700PPM=1EC…
Generally, you will want to measure the EC of your tap water then add no more than 1EC to that. Much much less for cuttings and seedlings. If you have added 1EC to your tap water and your plants are showing nutrient deficiencies, it is more likely you have a PH problem.