Casio rounding
11-13-2018, 01:19 PM (This post was last modified: 11-13-2018 01:20 PM by Pekis.)
Post: #1
 Pekis Member Posts: 120 Joined: Aug 2014
Casio rounding
Hello,

I found this in the Casio FX-602P manual:
What do you think of it ? I Wonder if it's specific to that model ...

11-13-2018, 04:24 PM
Post: #2
 Albert Chan Senior Member Posts: 1,992 Joined: Jul 2018
RE: Casio rounding
It is nice to see how well old manual does things.
Nowadays, this rounding stuff have to discover by yourself ...

Casio FX-115MS: 1E11 + 1 - 1E11 => 0, 1E11 - 1 - 1E11 => 0
Casio FX-3650P : 1E11 + 1 - 1E11 => 0, 1E11 - 1 - 1E11 => -1

Both Casio had a display bug:

e => 2.718281828
Ans÷10 => 0.271828182
Ans÷10 => 0.027182818
Ans÷10 => 2.718281828e-03
11-14-2018, 01:59 PM
Post: #3
 Eddie W. Shore Senior Member Posts: 1,358 Joined: Dec 2013
RE: Casio rounding
Interesting. The rounding scheme seems to be has been arbitrarily chosen instead of going with the traditional rule of looking at the last digit and rounding up when it is 5 or more.
11-14-2018, 03:39 PM
Post: #4
 toml_12953 Senior Member Posts: 1,917 Joined: Dec 2013
RE: Casio rounding
(11-14-2018 01:59 PM)Eddie W. Shore Wrote:  Interesting. The rounding scheme seems to be has been arbitrarily chosen instead of going with the traditional rule of looking at the last digit and rounding up when it is 5 or more.

For statistics, the rule is round to the nearest even digit:

Round to one decimal place:
5.55 ==> 5.6
5.45 ==> 5.4

Tom L
Cui bono?
11-14-2018, 04:28 PM
Post: #5
 ijabbott Senior Member Posts: 1,185 Joined: Jul 2015
RE: Casio rounding
(11-14-2018 01:59 PM)Eddie W. Shore Wrote:  Interesting. The rounding scheme seems to be has been arbitrarily chosen instead of going with the traditional rule of looking at the last digit and rounding up when it is 5 or more.

I think it's just the usual trick that some calculators do to "correct" small round-off errors instead of leaving them alone. However, these "corrections" can make the result worse. For example, 920/99 would produce an internal answer of 9.29292929292 or 9.29292929293 which the FX-602P would round off internally to 9.29292929300 before any subsequent operations were performed on it. (I haven't tested this on an actual FX-602P.)

— Ian Abbott
11-19-2018, 01:46 PM
Post: #6
 Eddie W. Shore Senior Member Posts: 1,358 Joined: Dec 2013
RE: Casio rounding
(11-14-2018 03:39 PM)toml_12953 Wrote:
(11-14-2018 01:59 PM)Eddie W. Shore Wrote:  Interesting. The rounding scheme seems to be has been arbitrarily chosen instead of going with the traditional rule of looking at the last digit and rounding up when it is 5 or more.

For statistics, the rule is round to the nearest even digit:

Round to one decimal place:
5.55 ==> 5.6
5.45 ==> 5.4

I don't think I was familiar with this method (Banker's method if I recall correctly) until Richard Nelson's talk about rounding methods at HHC 2018.
11-19-2018, 03:05 PM
Post: #7
 toml_12953 Senior Member Posts: 1,917 Joined: Dec 2013
RE: Casio rounding
(11-19-2018 01:46 PM)Eddie W. Shore Wrote:
(11-14-2018 03:39 PM)toml_12953 Wrote:  For statistics, the rule is round to the nearest even digit:

Round to one decimal place:
5.55 ==> 5.6
5.45 ==> 5.4

I don't think I was familiar with this method (Banker's method if I recall correctly) until Richard Nelson's talk about rounding methods at HHC 2018.

I think it's popular with statisticians since it tends to reduce rounding error when given a large sample population.

Tom L
Cui bono?
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