XPost: sci.electronics.equipment   
   From: presence@MUNGEpanix.com   
      
   In sci.electronics.equipment Commander Kinsey  wrote:   
   > On Sat, 20 Jun 2020 16:24:41 +0100, Ralph Mowery  wrote:   
   >   
   >> In article , CFKinsey@military.org.jp says...   
   >>>   
   >>> I'd need to contract OCD to understand that.  There's only one thing in   
   question here, how close is the reading to the correct value.  You can't split   
   that into two.  3.1416 is better than 3.14, and that's it.  All you can state   
   with a reading is it'   
   s correct to within a certain percentage.   
   >>   
   >> Try this.   
   >>   
   >> A doctor does a very complicated operation on your left arm like a joint   
   >> replacement.  It all goes very well.  Very precise.   
   >>   
   >> However he should have done the operation on the right arm that was   
   >> causing trouble.  Not accurate.   
   >   
   > Nope, because the first one is 100% useless.  I wouldn't call that precise   
   at all, as he was out by half a metre.   
   >   
   >> That is why a voltmeter can show 3 digits and be accurate to only the   
   >> last digit being in question by one number either way, but a 5 digit   
   >> volt meter can show many numbers, but if it is not calibrated corrctly   
   >> the 2nd digit to the 5 th digit  could be way off and the meter not   
   >> accurate at all.   
   >   
   > Showing those extra two numbers is pointless if they're wrong.  All that   
   matters is how many volts difference between the actual voltage and what is   
   shown.   
      
   agreed. The problem with the bullets and the target story is that when   
   explained, we somehow perfectly know where the bullets are- be in on   
   target or a small grouping somewhere else. Cheapo meters won't give   
   CONSISTENT or REPEATABLE results, not matter how "precise" they pretended   
   to be, or how accurate the spec sheet claims, especially considering the   
   last digit(s) may be totaly wrong, and random. It's like having crappy or   
   dirty test leads or a component. You'll get all the digits in the world,   
   but they keep changing. You won't even be able to pick a reading.   
      
   Keep in mind that "calibrated" equipment doesn't even have to be precise   
   or accurate. An example would be an adjustable power supply with digital   
   readout. Say it's always reads high by 0.7 volts. It's not precise or   
   accurate, but by knowing the offset it can used with success and may even   
   have great regulation.   
      
   On the other hand say you have an alibaba special power supply that's   
   "accurate" to +/- 0.35 volts, with terrible regulation that oscillates.   
      
   What power supply is better?   
      
   So the point is cheapo equipment can have lots of bogus digits and   
   readings that flop up and down, while better equipment can be more   
   consistently wrong, which can be compensated for. Precision and accuracy   
   mean little by themselves if you need multiple readings.   
      
   --- SoupGate-Win32 v1.05   
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