Change default character in decimal tag

[CC=Bill]

Using LibreOffice 5.2.5.1 on MS Windows 7
Conventional English usage is of a point (.) to denote the decimal place, the comma (,) being used to separate the thousands. The character default setting for decimal tags appears to be the comma. All documents involving columns of figures are apparently shifted to the default comma setting when saved, so that on re-opening, to update for example, columns are all over the place. One has to 'Select all', then reset decimal tags and change 'character' from comma to stop. How does one change the default setting?

[FJCC]

Go to the menu Tools -> Options and expand the Language Settings list on the left. Click Languages. What is your Locale Setting and is the Decimal Separator Key set to Same As Locale?

[CC=Bill]

Thank you FJCC. Your solution is entirely logical but does not work. Procedure followed 4x with a OpenOffice re-opened each time, but the re-opened table always shows alignment at the comma. Using 'Select all' on the document, correcting decimal tab settings, then using either 'Save' or 'Save as' still results in the error. If all the commas are removed, figures open to the LHS of the imaginary decimal tab line, which at least give a neat appearence.