Range plot on profile page: Nautical Miles or Statute Miles?

FlightAware ADS-B Flight Tracking
11

Let me show with an example what I suspect is happening. For the sake of simplicity lets work with a value of 100 and use the following abbreviations: nm = Nautical Miles, mi = Statute Miles, km=Kilometers.

First, a value of 100 gets written into the database. Note that this is just a value without any meaning. It could be dollars, peanuts or indeed some unit for a distance. It is up to the programmer to attach a unit to the value of 100 and thus give it meaning. Some sophisticated reporting systems allow the recording of the unit together with the value. In such cases, the meaning of the value is always clear. But when only a value is recorded, the meaning or unit of that value is open to interpretation. It may be in the head of the programmer or written down in some comment in the code that deals with the insertion of values into the database.

In any case, a value of 100 is now present in the database and lives there happily without any meaning or unit.

When the time comes to extract values from the database for display purposes, the unit which should be attached to the value of 100 becomes important again. Obviously, the unit should be the same as when the value was written. But this is not guaranteed. If the same programmer writes the insertion and extraction/display code, then you hope that he remembers and uses the same units for both operations. If two different programmers work on the different code sections, then you hope that the unit is documented somewhere and both persons attach the same meaning to the value of 100. But what happens when that link is not there and values are interpreted differently at different sections in the code?

Here is what can happen:

  1. Value 100 is saved with meaning ‘mi’
  2. Value 100 is read with meaning of ‘nm’
  3. 100 nm is converted according to user settings into the following: 100 nm, 115 mi or 185 km

This way, the original range value of:
161 km / 100 mi / 87 nm
“magically” turns into:
185 km / 115 mi /100 nm

That’s an artificial (and erroneous) increase of 15%. And no antennas, filter or amplifiers were needed for that :wink:

Edit: I just saw that you opened an internal ticket for that. Please forward the above to them; it may be useful. Thanks!