Weighing can be SUPER frustrating. I have had several eggs lose WAY MORE weight than they should have and hatch great.
BUT I would recommend it for dark eggs. Just a small kitchen scale will do. You take the weight when you set them (or at any point, you can start in the middle) and then they should lose .65% each day.
So let’s say you have an egg that weighs 2.00 ounces whenever you take the measurement. After 7 days, it should lose 7x.65% or 4.55%. So 2.00 (starting weight) Times .0455 is how much you want to see lost. That’s .091. Your egg should weigh 1.909.
You can do this after two or three days, just multiply the number of days by .65% to get your formula.
If your number is higher, you aren’t losing enough weight and you need to decrease your humidity. If it is lower, you’re losing too much and you need to increase your humidity.
I usually pick the couple eggs I want to hatch the most and base the humidity off of those egg weights. Air cells on fresh eggs are super tiny. I would get a white egg even from the store if you don’t have one of your own and candle that, fertilized or not, to practice finding it.