Hi,I read the instruction booklet again last night before going to bed.If the temperature is up to 2 marks above or below the thick line(100 deg F)it is ok.
Any more or less,you do need to adjust it,to adjust it,at the very top of the clear cover,you've got the blue plastic circle.It has a triangular section indented.In there is the small hole,use a screwdriver,it has a plus sign to the one side,clockwise for raising the temp.Obviously,the other way lowers it.The little + and - sign makes it very easy.
I think with these they are more humid,when new(which doesn't make sense to me)and after they've been used 3+ times,the humidity level can lower.
All my incubators are in a very humid room,so far I do not need to add water to any of mine for incubating,just hatching.
I use the covatutto 7,brinsea eco and covatutto's novital 24.I have good results from all of these 3 cheap incubators,even with serama chicks,that are meant to be very difficult.