Bob, maybe you can tell us about the difference between accuracy and
precision and which of the two concepts is  most relevant when determining
how many decimal points to use on a measuring instrument.

-Kent-

> -----Original Message-----
> From: SouthEast US Scuba Diving Travel list
> [mailto:[log in to unmask]]On Behalf Of Reef Fish
> Sent: Thursday, September 21, 2000 1:53 PM
> To: [log in to unmask]
> Subject: Re: [SCUBA-SE] UBS stick?
>
>
> On Thu, 21 Sep 2000 13:13:03 -0400, Lee Bell
> <[log in to unmask]> wrote:
>
> >Reef Fish wrote:
> >
> >> The UBS shows the O2 percent to ONE decimal place, e.g., 32.1.
> >> The Handi is SUPPOSED to be more accurate than the UBS.
> >> Now ask the manufacturer WHY it shows the O2 percent ONLY to two
> >> integers, with NO decimal place, e.g., 32, 33.  Is one supposed to
> >> GUESS what the correct decimal place is?  That's my "anecdotal
> >> information" about the Handi.  Save your money on this toy,
> Crusty.  :-)
> >
> >The answer to that question might be enough to keep me from buying the
> >Handi, if I didn't already have the stick,
>
> Lee saw my point about WHY a manufacturer claims superiority in accuracy
> but SHOWS only calibrations to integers in PERCENT O2, when most other
> calibration sticks or boxes show one decimal place.  Who can TELL how
> accurate or inaccurate its 32 percent is, if it could range from
> 31.51 to 32.49 percent.  That's a range of ONE percent -- and relative
> to 32%, it's approximately a THREE PERCENT ERROR.
>
> For the numerical-analysis challenged, percent error is 100 times
> Abs((true value - observed value)/(true value)).
>
> Now I wait with baited <sic> breath on the answer Strike got from the
> manufacturer of Handi on this -- if Strike hasn't forgotten to ask. :-)
>
>
> > but reading only to the nearest integer wouldn't.  O2 toxicity and
> > N2.loading being as variable as they are, the effects of temperature
> > and humidity on readings and the improbability of getting exactly the
> > same gas flow across the sensor twice in a row suggest to me that the
> > nearest integer is close enough.
>
> I wouldn't have to go into any pedantry to say for PRACTICAL purposes
> the nearest integer plus or minus two wouldn't worry me at all.
>
> So ... WHY are we quibbling about which instrument is the MOST ACCURATE?
> THAT was my point relative to Handi's selling point of "accuracy".  KISS
> principle should, and does, rule.
>
> -- Bob.
>