Do you live at really high altitude..? It shouldn't really matter in normal ranges.
The DarkSky application does give you altitude atmospheric pressure but you need to open the forecast to get at it and it may vary of course if it's wandering around and picking 2 or 3 locations close by.
What not just put up a Barometer in the kitchen..? (I'm presuming we aren't talking about some portable Microwave here )
If you haven't already started developing your barometric warning milk boiling app you could just leave a plastic spoon in the microwave vessel. And use a larger vessel. In the event that you've already started, please keep us up-to-date.
Interesting thought! Hmm. Unless a big storm has come in (low pressure system) or you live in a mountain valley with high winds (Venturi effect), the day to day boiling point of water should only change a few tenths of a degree day-to-day.
I wonder if the microwave oven is not as precise with its own timing cycle of the magnetron. Another variable there is line voltage at your house which can certainly fluctuate with demand on your local power grid. That would change the microwave power output accordingly, and perhaps substantially.
Before writing software, you might try to track these variables:
- Starting temperature of the milk
- Barometric pressure
- Line voltage at outlet (use a Kill-a-Watt meter or similar)
If you want to get precise, go pick up a Thermapen for your temperature measurements. Lovely tool to have in the kitchen.
There are electric milk warmers that stir and warm milk to a set temperature. Nespresso makes one, for example. They typically shut off automatically before even scalding the milk.