From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: Fuel Burn et al
To: lml
Date: Sat, 05 Mar 2005 15:28:43 -0500
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Posted for "Jim Nordin" <panelmaker@earthlink.net>:

  Gary did a pretty good job in my view. And I'd like to further the
  discussion with reference to accuracy.
  
First I want to tell you all I have no flame suit. After seeing recent
  messages on various subjects, I hesitate to make comments on the LML,
  perhaps others do as well. This is bad. But I'm going to make these and see
  how it goes.
  
  There is a perception, by many, that accuracy and precision is one in the
  same. While precision is not a topic of this discussion per se it might be
  good for everyone to have an appreciation for both, thus bringing all of us
  to a level understanding of both and we will all be better to express our
  views and ideas. Recently I read an article regarding accuracy and precision
  as it refers to GPS. Which also might be worthwhile having an appreciation
  for. [I've been trying to educate friends on the "accuracy" information on
  GPS packaging and literature for a long time.]
  
  Accuracy is a measure of the closeness of one or more "rate of burn"
  readings to a "rate of burn" that's known and defined in terms of an
  absolute reference system (how many gallons were left perhaps). The known
  reference often is referred to as the "true reference point" or in this case
  "rate of burn". Accuracy compares different measuring devices to a true
  "rate of burn", and hence to one another. [I guess to do this properly, one
  would have to get to altitude on one tank, switch to another tank, take the
  rate of burn readings onboard during steady state flight, switch to another
  tank after a measured period of time, land and determing delta gallons in
  the tank used during the reading period. Compare the rate of burn indicated
  on board with the usage over time as measured by fuel remaining.]
  
  Precision is a measure of repeatability indicating how closely several
  "rates of burn" readings fall within each other. Precision is based on a
  relative reference system that's unique to the device making the
  measurements.
  
  You can give the analogy:
  
  When dealing with target practice with a bow and arrow.
  
  If there is a tight grouping of arrows on the target in the upper left
  quadrant near the edge of the target, that grouping is said to be a precise
  grouping. Poor accuracy perhaps.
  
  Notice the tight grouping missed the bull's eye significantly. If a looser
  grouping were found around the bulls eye and the convergence was near the
  center of the bull's eye that would be said to be accurate. [Right on
  target?] Poor precision perhaps. If you were trying to hit a water filled
  balloon to deflate that balloon, you would want an accurate precise hit. For
  hitting all around the balloon might be categorized as accurate, you still
  didn't burst it.
  
  If a tight grouping of arrows were found in the bull's eye, that would be
  said to be an accurate precise grouping.
  
Fly safe by establishing all limitations, accurately and precisely.
  
  Jim