Congratulations! I am sure glad that one of those chicks wasn't the egg you cracked open! Keep us updated on how many hatch. What kind of chickens are they?
I know your incubator instructions say 99.5 That is what the temperature of the egg should be when incubated.
However with a still air you need to have it like Cammy said at 101.5 to 102. Because your incubator does not have a fan, the temperature in there changes and that is why you need the temps higher.
Your hatch took 24 days and that is also an indication to raise the temp if you can.
It should take about 21 days.
Well, you have some chicks and you should be officially "hooked" now!
It is very good that you are going to get a hygrometer. And yes the thermometers vary alot. I always use a couple and compare.