First let me start by stating that by increasing the light intensity, you encourage your plants to absorb even more CO2 which increases growth and yield. When the plants receive between 4500-5500fc (48,240 lux) of light, they can utilize between 1200-1300 ppm of CO2. While very few gardens are supplied with more than 7500 fc (80,400 lux) of light, at that intensity the pants can use up to 1500 ppm of CO2.
At the light intensity of 600 mol (4600 fc) (49,310 lux), the photosynthesis rate increases more as CO2 concentrations are increased to 400 ppm. The rate of increase declines a bit after that, but the photosynthesis rate continues to increase as CO2 levels reach 600 ppm. Above 600 ppm of CO2, the photosynthesis rate continues to climb but at an even slower rate, until the rate increases levels off at about 1200 ppm.
So that meter would be a nice toy
Now Water PPM expressed as (EC) meter luxury reasons here's my explanation. the meters measure how efficiently electrons travel across probes through the solution. Pure, distilled water conducts virtually no electricity. The more nutrients and minerals in the solution, the more electricity is conducted. So for foliar feeding applications it is essential to use 250-500 ppm is typical (EC 0.5-1.0mS).
There are some small example, sorry it took so long and wasn't as detailed as could have been, but Im getting family ready for bed, hectic. sorry it took so long and wasn't even probably very detailed. Just trying to an example of why meters are always nice to have.
I should have not even gotten into this its late im tired.