1) Since the early days of aviation, barometric pressure has been the common standard reference for pilots so that they know their altitude above sea level. This is particularly important so that air traffic control can provide vertical separation between aircraft. Of course, local barometric pressure varying slowly over time with changing weather, so pilots need to periodically get the current local altimeter setting from the weather broadcasts and adjust thier instruments to the new setting. avAltimeter is the first and only app to allow a pilot to adjust their app altimeter to the current setting.
2) Apple introduced the barometer sensor into the iPhone starting with the iPhone 6. The earlier phones did not have that hardware. Apple iPads earlier than the model 4, the mini 2, or the iPad Pro are also missing the sensor. avAltimeter works with all later models.
3) To enter a new altimer setting, tap the adjustment knob in the lower left corner of the altimeter image (ok, ok, anywhere on the image of the altimeter). The tap will bring up a “picker” control where you can drag the digits to get the barometer setting you desire. When set for imperial units, enter the new pressure in inches of mercury. When in metric units, enter the pressure setting in millibars. when you have selected the digits you want to enter, just tap outside the control, back on the adjustment knob again. The entry control will disappear and the new setting will appear in the Kollsman window on the face of the altimeter.
4) In the grey datablock there is a white entry area next to the OAT (outside air temperature) label. Tap the white entry area and a temperature “picker” control will pop up. Drag the digits to select the desired temperature setting and then click the done button above the digits.
5) Sorry, you can not. avAltimeter uses the FAA regulations altitudes. FAR 91.211 says:
6) When the pressure altitude exceeds 12,500 feet MSL (mean sea level) the O2 Warn starts flashing red and a 30 minute timer starts. The progress of the timer is shown on the bar next to the O2 Warn text. As long as you stay above 12,500′, the timer keeps counting and, if turned on, a voice alert will prompt you about needing oxygen. When the timer gets to 30 minutes the O2 Warn text will stay red and the voice warning will change to “Oxygen Now!”.
Any time you exceed 14,000′, the “Oxygen Now!” alarm will sound and the O2 Warn text will turn solid red. The alarms will reset as soon as you descend below 12,500′ and the timer will reset after you remain below 12,500′ for more than 5 minutes. Remember that this App is not certified by the FAA to be accurate and is not warranted by the developer for any purpose at all. The app may give you a friendly reminder when you are operating at high altitude, but it can not be relied on. It is not a flight instrument!
7) The voice alarm can be disabled or re-enabled from the settings page.
8) The units for display and for data entry can be switched from imperial to metric on the Settings page.
9) The propellor setting improves the accuracy of the estimated take off distance for a given density altitude. See the website created by Sparky Imelson, one of the great teachers of Mountain Flying.
10) Density Altitude is dependent on both Outside Air Temperature and humidity. Generally speaking, during flight, an Outside Humidity reading is not available, so avAltimeter calculates the Density Altitude based on dry air. Expect the true density altitude to be higher by as much as several hundred feet in high humidity conditions.