Originally Posted by

**Akrnaf2** This is a translation of a post that I have written in a forum in Israel that I am one of its admins. I hope it will help thous that cano't see the development of the air cell in a very dark shell eggs:
Anyone who incubate eggs know that one of the most important parameters except the incubation temperature, is the humidity.

The accepted convention says that incubation eggs (in the first 19 days) should have humidity of 50% and during the hatching (days 19-21) humidity should move around the 75%.

I would like to say that such determinations are not absolute!

We must remember that moisture is the only means of bringing the egg weight loss necessary for the development of air cell. Chicken eggs have to lose 11-13 percent of their weight from day 1 to day 19 of incubation. This is the percentage that allows the creation of proper air cell and normal development! If the egg does not lose weight at the appropriate rate that the an air sack will develop properly, mean that the incubator humidity is too high and we need to reduce it! And if it losses weight that is higher than 11-13 percent and the air cell is greater than that needed, means that the humidity in an incubator is lower that what is needed, and we should raise it! The correct way to determine the correct incubation humidity present is to calculate the future weight loss of of the egg.

And the way to calculate this is:

You should weight the egg before entering it to the incubation. After the first 4 days ,in the first candling you weight it again. The gap weight (starting weight less weight on the fourth day), you divide the initial weight of the egg, the result should be multiplied by 100, that is the percentage of weight lost, percentage, for four days. Daily weight loss percentages can be known by dividing the result by 4.

To know the expected rate of weight loss of the entire incubation period you should multiplied the percentage of daily weight loss by 19. and this is the expected weight loss over the incubation. If it is between 11-13 percent humidity you are good, If it do not, you should correct the humidity levels!

for example:

If the initial egg weight is 56 grams

And after 4 days is 54.8 grams.

So: the ratio of weight lost in 4 days is:

0.0214 = (56 - 54.8):56

Multiple the result by 100

And This Is considered the weight loss percentages for 4 days:

0.0214 * 100 = 2.14%

2.14% are weight loss in 4 days. So to know the daily weight loss percentages is:

2.14% : 4 = 0.54%

Calculate the percentage of weight loss per incubation period (first 19 days):

0.54% * 19 = 10.3%

This humidity Value of 10.3% is lower than the minimum of 11% percent required, it means that probably that humidity in the incubator was higher than necessary and you have to reduce it!

Good luck