XPost: sci.electronics.equipment   
   From: nobody@nowhere.com   
      
   On 6/20/2020 9:28 PM, 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.   
   >   
      
   You keep saying that it's only the accuracy that matters. That's   
   true to some - and only some - extent.   
      
   Now let's compare two different hypothetical meters, both 100%   
   accurate. Let's say that meter A has 3.5 digits (max count 1999)   
   and meter B is 4.5 digits (19999). Use them to measure a battery   
   cell of exactly 1.612345V.   
      
   Meter A will display 1.612V whereas meter B will show 1.6123V.   
   Meter B allows you to evaluate the result to a higher degree of   
   precision.   
      
   Further suppose that both meters are not perfectly accurate and   
   read 1% low. A will show 1.596V while B will read 1.5962V. B is   
   still more precise in showing you what it thinks the voltage is.   
   An order of magnitude more precise, in fact, even though both   
   meters are off by -1%.   
      
   That's how the term 'precision' is used in engineering. Perhaps   
   what's confusing you is the fact that the term is more loosely   
   applied in everyday language.   
      
   As to the +/- 3 count (or 1 or whatever) possible error, it's an   
   *uncertainty*, not a fixed inaccuracy, in digitizing an analog   
   quantity. It will take too long to explain in detail here. Let me   
   put it this way: If you measure the example voltage above   
   multiple times with a meter with +/-3 count uncertainty, you may   
   get a reading that varies from measurement to measurement by up   
   to 6 points in the last digit. That's not a percentage inaccuracy.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)