I use Taylor digitals, Accurite digitals and Flukers. I will tell you that it is not always the accuracy of the instrument but doing test hatches to figure out what the right setting is. By doing a test hatch, you can monitor the air cell for humidity, hatch date for temps and so on. It is really trial and error until you get it right. The instruments just help you try to manage it and I promise you will never find one that is right on the mark.
For example, I have an Accurite that reads 98.6, but the chicks hatch on time..so that is the setting I use when I use that instrument. I have others that read over a hundred. As long as the hatch goes right, I know the settting is right. I guess my point is, it's not the exact number that you need from an instrument compared to the incubating instructions..it is what makes the hatch successful.
Jody