Here is one way:
Type "1" in the first cell of the column
In all other cells of column A paste a formula.
The formula adds 0.1 to the previous cell. When you change chapters, manually type the new chapter number.
A1 contains "1" (no double quotes)
A2=A1+0.1
this is shorthand for, select cell A2, then type (or copy and paste from here) the formula:
=A1+0.1
select A2, copy
select cells A2 thru the end of the column, paste
now simply type the number on the row when the chapter changes. If you type over a formula later, select a cell in column A with a formula in it, copy, then select the cell (s) you typed over, paste
You can get fancier and only show the chapter numbers when there is information in columns B, C, and D but that gets harder to keep straight. Depending on how you work the fancier way could be helpful.
Finally... I should address switching the comma to a period. Add a new column after column A and enter the formula:
B1=SUBSTITUTE(A1; ","; ".")
Again, this is shorthand for, select cell B1, then type (or copy and paste from here) the formula:
=SUBSTITUTE(A1; ","; ".")
later on, you can hide column A