Dew Point: Vent Check

You already have the readings. This tells you what they mean. Type in what your own thermometer and hygrometer say — for this room, and for the air you are thinking of letting in. Nothing here is measured by the phone and nothing is fetched from a weather service. There is no network code in this app at all. Compare rooms by moisture, not percent. Relative humidity moves with temperature even when the water does not. Outside at 5 °C and 90 % holds about half the water of a room at 21 °C and 60 % — so opening the window in winter dries the room, and the percentages say the opposite. Both states sit on one axis in grams of water per kilogram of dry air, and the answer is a direction with a size, not a number to interpret. What the room becomes if you vent. Slide how much of the other air to let in and the mixed state moves between the two: its temperature, its humidity, its dew point.…