Hey, I needed a CYA kit refill, so I ordered the 50ppm Standard. (They give way too much of it, as for training a single sample is adequate.)
As I suspected, the 50ppm Standard reads 40ppm by my eye, and in order to get the dot ABSOLUTELY obscured, it reads only 30ppm.
Granted the scale is logarithmic, and so smaller ppms will be less accurate than larger ones.
I added the required 70oz of stabilizer this week (2 very full sock loads), and hastened the distribution by kneading it in the sock while moving around in the pool.
Hope to see 70ppm by my eye later in the weekend.