XPost: sci.electronics.equipment   
   From: presence@MUNGEpanix.com   
      
   In sci.electronics.basics Commander Kinsey  wrote:   
   > On Fri, 26 Jun 2020 05:54:19 +0100, Cydrome Leader    
   wrote:   
   >   
   >> 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.   
   >   
   > I've got thermostats like that, I've calibrated them to 0.1C.  Trouble   
   > is, they have remote sensors which work perfectly, but if the actual   
   > unit gets very warm (as in direct sunlight), the reading goes up by as   
   > much as 2C.  Nevermind, they happen to be in my conservatory (the main   
   > source of heat in the summer), along with the air conditioner, so on a   
   > hot day they switch it on slightly too soon, then correct themselves   
   > when the AC cools them off.   
      
   Is it the controller that's off by 2C when it warms up?   
      
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