Graphing Calculator on Android produces wrong results ! (compared to web)

dsnz shared this problem 1 year ago
Not a Problem

if you run the design of the attached file you will get different results on web and on Android


on web the results are


Cf = 0.00593


AB = 24.09566


and they are correct


on Android the results are


Cf = 0.02892


AB = 24.04689


and they are wrong


this is serious because these are simple basic calculations and may have financial/other serious consequences for people who depend on them (some use the apps beyond education purposes, e.g. building/construction/topography etc.)


NOTES:


1. Android is Android P latest (Android One) and latest update of app


2. the attached ggb file has been produced by the web version, input data are with 2 decimal places, on Android I can't sign in and save/sync (this has been mentioned in forums more than one month now) and also I can't find an option to open a ggb file, the content is very simple that you can enter manually on Android app and test

Comments (5)

photo
1

The easiest way to load on Android is using a link to the file eg https://www.geogebra.org/gr...

photo
1

I don't see the bug with https://www.geogebra.org/gr... - what results do you see for that?

photo
1

Hi,

I followed your link and indeed it opened on Android, and even the text size became 16 pt as on web, and however I tried I got correct results ! Even if I started from a new state (by clearing everything) and inputting by hand I still get new results (remember this is a ggb exported from web).


As I was becoming crazy :) I remembered I had managed to save a .ggb locally on Android by the share option in my first attempts. It's a first edition code having only the Cf distance calculation and in that edition I worked with bigger numbers, where all X are plus 500 and all Y are plus 200 and later I removed the leading digit in order to simplify the numbers, but still the result should be the same (except for the line formula of course). I opened this file on Android and web and get wrong results in both, even if I delete a Point/Line/Distance and reenter it. So, it seems that it some calculation that gets stuck internally and affects the result and this has been captured internally in the ggb file.


Note: on web, after loading the Line and Distance formulas display first and then the rest. I don't know why, on Android they display in proper order (I managed to load the ggb on Android not from the menu but using a file manager and then selecting the Graphing Calculator from a list of apps to process it).


I hope you can replicate this and perhaps by examining the ggb file understand the issue.

photo
1

I think you've just mis-typed the .32 / .23 here:

B = (62.32, 48.99)
B = (262.23, 548.99)

photo
1

Yes !

I checked now and you are right. Never work at night with many calculations again !

I'm sorry for the wrong alert.


Thank you,

© 2020 International GeoGebra Institute