Hi Twig,
I don't understand what "proportional control heating" means (no explanation necessary. You could explain it, but it's like I tell Hubby when he's explaining his design stuff '"Thanks, but I don't want to hear the details).
I just know that measuring air temps at egg height grows and hatches chicks.
It is unnecessary to *know the internal egg temp* IF air temps at egg height are right.
I remember when the 'water weasel/ wiggler' came into being as an incubator *must have*.
I say the same thing now as I did then --- if you have room in your bator and want to know *just because*, just don't use the 'that reading' as your only measure of temperature.
Good luck,
Lisa