Sorry if this sounds dumb but why do you use a refractometer?
in the orchard I can tell general health of my pears, apples, cherries,grapes etc by testing with it. the device shows me how much sugar is in the leaf or fruit parts of the plant=brix. for instance I wont harvest my apples until I see the highest brix of the season, or my grapes etc. much sugar tastes good in fruit.
in mj high brix plants are less susceptible to pest and can show healthy by indicating burned and unburned carbs in the plant material.. I aim for high brix until the end stages of development, when I aim to have those excess sugars converted into energy for the plant right before harvest. This is why some people need to ferment their weed in jars after its dry even. A super healthy mj pant with high brix is not ideal to harvest, feeding should be timed for the reduction.
the excess sugars taste nasty, burn shitty. but when the ferment uses bacteria to consume those sugars/carbs making the weed less harsh on the lungs. feed less, ferment less? the tool lets me see exactly whats going on during the life of the plant with uptake, excess nutrients, etc. its used for other things too, like blood plasma, saline, antifreeze, etc.hope helps