Created attachment 87031 [details]
Small Calc spreadsheet. Shows incorrect cell calculations

It is possible that the error described below is due to the limitations of my HP desktop computer chip set.
It may not be able to handle very long numbers accurately.
I seem to recall this was a computing issue as long ago as the 1970s but I thought it would have been resolved by now.

The desktop has the following characteristics:
Processor: AMD Ryzen 5 3500U with Radeon Vega Mobile Gfx     2.10 GHz
Installed RAM : 8,00 GB (5,95 GB usable)
System Type: 64-bit operating system, x64-based processor
Operating system: Windows 10 Home.

Look at attached Open Office Calc “spreadsheet summation error02.ods”
I have a reason for wanting to display the group of numbers in Column E in the manner shown.
Each row represents the “building blocks” of the  19 digit number  1,101,319,202,932,383,948.
The cells E1 to E19 are  summated in cells E21 and E22.
E21 sums the range (E1:E19) and, as a check, E22 sums the individual cells E1;E2;E3 etc.

Both results are incorrect.
They show the sum as 1,101,319,202,932,380,000
What happened to the 3,948 that should be included in the sum?

I tested the calculation in Column G to find at what stage does the error occur.
Note that the sum of the numbers in cells G1 to G16 is shown in Cell G21 to be 1,319,202,932,383,950
The last three numbers in the total should be 948.

It seems that the calculation begins to go awry (or is rounded) when 16 digits are reached.
Over to you, boffins.