hmmm but i agree with what you say.
1) the optimum is 40-50% and its not an issue with how the dry cabi works but rather the optimum protection against two types of mold/fungus.. cos one type like high humidity and the other type thrives in 20-30% RH
that's the other not often talked about reason for keeping RH at a optimum and not jus about protecting the oils in seals from drying up..
but i can't verify this as i read this from somewhere way back..
2) the pt mentioned is subjected to the affinity of sllica gel for moisture so its not to be taken as absolute terms like zero humidity (very hard to achieve)
3)the cobalt chloride in the gel just indicates the amt of moisture absorbed by the gel..
hence i say its an indirect way of 'measuring' the humidity in a closed system. so if the dry cabi is working fine, by right ur silica gel in the cabi shld not turn pink as the humidity shld be taken care by ur dehumidifier.
if it does turn pink it means ur dehumidifier is spoilt.
if it turns pink and ur hygrometer says its ok then ur hygrometer and dehumidifier is spoilt assuming ur cabi door is sealed properly.
anyway the issue is down to individual preference.
I find that keeping a space and a power plug for a dry cabi a chore i rather not deal with.
but a dry cabi offers a nice presentation of ur gear in a dust free (if u close the door and clean it) and low RH environment.