rustyswoman,,I too was very concerned at first trying to decide the correct humiditity to hatch marans eggs.Given the fact if the eggs was under a hen,outside humiditity levels change all the time,,with weather fronts coming in,,rain,fog,ect! The hen cannot control this in nature,yet we look for the optimum setting to insure our mechanical device closely mimmicks a hen setting on the eggs.I weigh every egg before it goes in the tray,and write that weight on the egg,,(air sack side) and set the humidity level on 50%,,,and walk away. The scientists that makes a living doing this,says an egg should lose 10-12% of it's weight during the incubation process,,so at day 14 I will pull a few eggs out and weigh them,,many times with this humidity setting,my weight loss has been close to 9%,,which is close enough because I leave the 50% humidity setting the same,,,and another 4 days at this rate will lower the weight another 1-2%,,at day 18 I add 2 sponges to the water tray,,put enough water to almost fill the tray,set the rh level up to 55%,,,and then only open the door twice a day to add water to the tray,,
After I candle the eggs at 7-10 days,, I have a very high hatch rate with using these rh levels,,upwards of 90% with marans.I do pay very close attention with the time from when a chick pips,to when or if it zips,,12 hours and no progress is time to intervene.Seems if they pip a large hole and stop for a long time,is when I find the inner membrane has dried sometimes on their feathers,,and many times if there is a slow one,and a few other hatch,it seems this helps energize the slow one. Your only real way to know if settings are close is to weigh each egg before you start the incubating,,3-3.5% weight loss a week is perfect,,,but then again,a hen has no way to control her outside rh ,,,does she??
