Technically it could use some more advanced regex/filtering on the OCR output, you're right! I found that with some receipts, you actually can omit cropping with some exceptions. I'd definitely like to remove the need for cropping altogether.
You nailed all the limitations of this app (and others like it) on the head :) The reality is that there will probably never be a foolproof way to understand our consumption/nutrition habits 100%, so my goal with this was to make it easier to understand at a high level what was in my groceries (that didn't require individual scans of each product).
I'm sure most chains have the purchase tracking for ads/marketing, but not sure how their data incorporates nutritional/ingredient data (if at all).
I agree. Hopefully there will be a day where grocery retailers provide access to their product data APIs to make this a smoother process. Or if the store provided a QR code on the receipt so you could quickly see information similar to what's on GroceryTrip.
Quick and dirty solution: find the optimal position for the valve(s), mark where they are relative to their base, and open the valves to that position each time
I think OP is correct. Think about the extremes of the urn, full vs 1mL in it. It will require much less energy to heat the 1mL state than the full state.
Regarding the contents, the thermal conductivity of liquid (Water mostly for coffee) is higher than that of air, so it transfers heat out of the urn faster than an urn full of air. It also has higher heat capacity which requires more heat energy per degree change of temperature.
Heat capacity is given by (C) = heat absorbed (Q) / temperature change (ΔT); heat capacity increases with volume