you only have to do it if the co2 levels in your room never drop down to 400. my grow room was my bedroom, so i enriched during the day (lights on), and slept in there at night (lights off) the co2 levels never dropped below 1000. when i first got the meter i read in the instructions not for use in areas of constant high co2 levels so i called the manufacture and they told me it has a auto calibration so if 1000 ppms is the lowest it senses for a week or so it will recalibrate 1000 to 400. they told me to take the meter outside once a week and manual calibrate it. now that i dont sleep in the grow room ppms drop to 400 at night and i dont have to worry about it.
thanks for stopping by hiker, i hope this info helps.