Thank you for your Help.
The comma separator is the clue. I needed to replace the comma with the dot.
The way I did it :
select the column with the number value formulated as Text
go to Edit select Find, Find
enter in Find " , "and in Replace with " . " (without the "). click on Replace all.
all commas changed to dot seperator
Close the Find window.
select the column again and go to Format in the Menu bar
select Cell
under Data Format select Number or Currency. Enter
and from hereon you can add, subtract and all other functions with Numbers
Note:
the formula you gave for S2 should be R2+0 otherwise the result changes by 1 as you can see in the last column