Sorry, I mis read, now I see what you are saying.I don't think I would keep hatching if I only got 50% most of the time.
A digital thermostat is TOTALLY different than the thermometers. I have those in there too. The thermostat will keep the temps correct. Mine has a mark that I SET to turn on when it gets to that low temp it comes on. Same way when it get to the right temp it goes off. My bator only swings about .5 to 1 degree EVER. Also what is your humidity and did you calibrate your hygrometer? Both are critical to good hatches.
We do need to upgrade the temp control ! Basically we've been using the dimmer switch and literally fine tuning it manually 24/7 but obviously that isn't even keeping it steady enough.
I'm going to try the LG on loan and see the results if it is better then I know it isn't my house, then I can try to build a better bator, or buy one. Right now there are so many variables including diff. eggs from diff. sources.
I did just candle the remaining eggs which are staggered hatch due sat (1 wk after the others) so 1/1 chicken & 5/6 duck , the chicken too dark to see, but the duck all had movement.
So to me it is really odd that 10 eggs died at or very near hatch, while 5 duck eggs remain alive - that does not seam to me to be just temps. but I'm certainly a newbie on incubating.