to be honest i never use a hydrometer in the incs, but go by the fact that an egg will lose 13% of it's weight over the inc period......if the egg gains weight the humidity is too high.
can i just explain the principle of weighing the eggs....?
all eggs will lose weight, whether they are in an incubator or under a bird.
you need to make a graph.
top of graph.......no of days for incubation.....
side of graph ....egg weights
an egg will lose 13% of its weight throughout incubation process.
calculate the 13% loss and draw your line on the graph.
if the weight increases above the line, then there is too much humidity.....and egg should be moved to a dryer incubator
if the weight falls below the line, too little humidity, and so egg should be moved to wetter incubator.
once you have calculated what is happening, you need only weigh one egg each time.
any kitchen scales will do as long as they weigh in grams.
VC