OK, so All plants use co2 and if you don't provide fresh air then they can't grow.
Without intake and exhaust you will run out of co2 quickly.
Nonetheless, to read the chart..
Temperature is on the bottom, go from there up to the humidity line and to the right for lb h2o/lb dry air for that temp/humidity.
Let's say it's 0.2 lb h2o per lb dry air..
So for 1.2 lb of air you have 0.2lb h2o/1.2lb air
If your tent was 4x4x4 ft that's 64 cubic ft.
Pv=nrt so n=pv/rt
1atm * 64cuft * (? Liters/cuft) /0.08206 * temp in kelvin
That's the number of moles of air. Multiply by the absolute humidity times weight of water summed with molar fraction bone dry air by 29g/mol to get the weight of air and then multiply by % bda and by lb h2o/lb bda and then convert the mass of water into a volume. Subtract volume of water removed from Humidifier and calculate new absolute humidity then follow that from the right side of the chart to your temp to see what humidity you're at.