Weighing
your eggs is the best way to make sure you've got the
humidity inside
your incubator
right. I figured some of you might find the idea
daunting, so I'll take you through it step by step.

First, you want to find
the weight of your eggs at the time you put
them in the incubator. There's no need to weigh one egg at a time
--- just put all of the eggs on a scales at once. If you're lucky
and your tray of eggs can be lifted straight out of the incubator (like
in our new Brinsea
Octagon 20), you can
put the tray and eggs on the
scales together. Then take the eggs out of the tray and weigh the
tray alone. The weight of the eggs without the tray can be
calculated using the following simple formula:

(Current
weight of eggs) = (Weight of eggs and tray) - (Weight of tray)

Our eggs and tray
weighed 59.8 ounces at the beginning of our
incubation period and the tray alone weighed 7.3 ounces, so the eggs
weighed:

(Current
weight of eggs) = 59.8 - 7.3

(Current weight of eggs) = 52.5

The next step is to
figure out how much I want the eggs to weigh at the
end of the incubation period. We're aiming for a 13% weight loss,
so:

(Goal
weight at end of incubation) = (First day weight of eggs) X 0.87

For our eggs, that is:

(Goal
weight at end of incubation) = 52.5 X 0.87

(Goal weight at end of incubation) = 45.7

It's also useful to know
what our daily weight loss goal is:

(Daily
goal weight loss) = (First
day weight of eggs) - (Goal weight at end of incubation)

21

Our eggs need to lose:

(Daily
goal weight loss) = 52.5 -
45.7

21

(Daily goal weight loss) = 0.324

(For those of you who
ran away from algebra, be sure to do the subtraction before the
division in the equation above.)

Now I'm ready to find
out if my eggs are on track with their goal
weight loss on a certain day. After two full days of incubation,
I weighed my eggs and tray again, subtracted out the weight of the
tray, and got a new weight of 51.8 ounces. Did I have the
humidity set right?

First, I calculate the
goal weight loss for the day:

(Goal
weight loss on a certain day) = (Daily goal weight loss) X (Days since
incubation started)

For my eggs:

(Goal
weight loss on day 2) = 0.324 X 2

(Goal weight loss on day 2) = 0.648

Next, I figure how much
the eggs should weigh now:

(Goal weight on a certain day) = (First day weight of eggs) -
(Goal weight loss on a certain day)

For my eggs:

(Goal
weight on day 2) = 52.5 - 0.648

(Goal weight on day 2) = 51.85

If
you remember, my eggs weighed 51.8 ounces on day 2, so if anything
they've lost just a hair too much weight. I had let the
incubator's percent humidity drop down into the high 30s that morning
since it ran in the low 50s the first day, but it looks like I need to
refill the well or close the vent.

I hope this math doesn't
look daunting! I promise, it's simple
arithmetic, and weighing your eggs every two or three days during
incubation should increase your hatch rates.

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Excellent point! I was actually thinking about significant figures and knew I was ignoring them as I did these calculations. On the other hand, after the first couple of days, that lack of accuracy becomes less important because the amount of weight lost will be higher, making a 0.2 or 0.3 ounce loss of accuracy no big deal. Within the first week, you should be able to see a clear trend as your egg weight continues to be below weight, above weight, or right on target.

What I have started wondering about this calculation, though, is whether I should be dividing the goal weight loss by 21 days or by 18 or 19. My weight loss seemed to be consistently more than it was supposed to be even though I was keeping the humidity on target, and then I realized that around day 19, I'll be increasing the humidity drastically to prepare for hatch, which means that the egg won't lose much more weight. So I might revisit these calculations later, especially if I can find more data on weight loss over time!

Thanks for posting this! It was very helpful and clear enough for even me to figure out! Aloha!

Tonya

Very clear information thanks for posting, I am also using a Brinsea OCT20 so using the tray to weigh the eggs is definitely convenient. In regards to the # of day for chickens it would be 18 days, for me since I just put duck eggs in my incubator a couple of references I have say 14% weight loss by day 25, after which humidity goes up during lockdown for the last 3 days.

Clint --- That's what I decided too, eventually --- that I wanted 13% weight loss by day 18. I started getting really good hatches once I figured that out!

Good luck with your duck eggs! I've got some chicken eggs pipping as I type.