1. On Yom Tov, what is the lowest effective target temperature for the oven, for example 100 degrees, such that a Jew can still decrease the tweaker offset so that the oven will eventually increase to a baking temperature? Perhaps anything above room temperature is enough since the control loop would on its own ignite the fuel? Or perhaps it must remain above Yad Soledes Bo?

(Rav Mushell said there is no lower limit – even less than room temperature is okay – issur in question is the issur of havarah and the rabbinic prohibition of molid,, then there should not be need to be yad soledes, )

2. Must food already be in the oven?

(Rav Mushell said no - it is okay for the oven to be empty, and to preheat food)

(Rav Mushell in Rav Heinemann's name said yes - the total delay is sufficient that we do not need to check the glow bar before changing the tweak offset)

We believe the following built-in delays may be relevant:

A. control loop averages temperatures over time, so no immediate response to decreasing tweak offset. Multiple samples polled to rule out errors.
B. tweaker does not directly turn on or off the glow bar ignitor
C. the gas valve has to open only after the glow bar is hot
D. gas ignites only after gas valve opens, and stays burning after the valve closes until fuel in the tube burns out
E. additional gromma delay in the the Star-K approved control loop logic

4. Conversely, when food has been sufficiently warmed, and we wish to dial up a tweak offset which targets a lower temperature (such that a child could touch the oven door and less fuel will be wasted) is it permitted to increase the tweaker offset so that the control loop targets a lower temperature?

(included in Rav Mushell's answer to #3 presumably)

5. Must food still be in the oven?

(Rav Mushell said no - it is okay for the enjoyment of Yom Tov to lower the temperature after food is out and it is empty - consistent with #2)

6. Must changes to the offset be made when the control loop is at that time calling for heat?

(included in Rav Mushell's anwer to #3 presumably)

7. Can we rely upon the same (A - E) built-in delays (gromma?) to permit this?

(included in Rav Mushell's answer to #3 presumably)

8. If heat is on and we want it hotter, can we always safely back off the tweak offset so that the heat stays on longer?

(included in Rav Mushell's answer to #3 presumably)

9. If heat is off and we want it cooler, can we always safely increase the tweak offset so that the heat stays off longer?

(included in Rav Mushell's answer to #3 presumably)

We also have this extra credit question regarding Rav Shlomo Miller’s issur letter on Lakewood stationery:

10. Would this device be useful to add to a Shabbos-mode stove prohibited by Rav Miller’s issur letter so that someone could use their stove’s oven without violating the issur, since with this device no messages are sent into the programming of the oven controller, instead the system confuses the controller’s ability to accurately measure the oven temperature, and only results in a different effective temperature, without sending in messages to the computer?

Rav Mushell, in Rav Heinemann’s name, has provided these letters:

With regard to your system to instill a time delay, rabbi Heinemann felt it would be OK. This is assuming thee are no other issues in adjusting the temperature i.e. display changes etc. As to if this would satisfy Rabbi Miller's issues, I do not think so. My understanding is that Rabbi Miller believes that adjusting the temperature is a form of tikun maneh, Fixing a vessel.

Further, As the source for the built-in delays of 15 seconds on the glow bar:

Rabbi Heinemann is definitely of the opinion that the present delay is acceptable as programmed for those ovens using the Sabbath mode. The issue that Rabbi Miller has with the system is that he feels that by entering information into a system you are constructing of fixing something. The question is, where you have something that is designed to continually change. Can it be classified as tikum maneh or binyan. Rabbi Heinemann has proofs that this situation is not halachically classified as either and therefore permissible. He has told me that he will put these in teshuva form soon.

And further regarding the long standing difference on views:

I will show this to Rabbi Heinemann for comment. (However I believe that this is an old argument between Rabbi Heinemann and Rabbi Miller. Rabbi Heinemann believes that halachically you are not doing anything when leaving a magnetic image as it is not writing etc.)
Kol Tuv,
Avrohom Mushell