The numbering is free, but for ease of reference, the default items have been numbered according to the following logic:
Items starting with 1000 refer to units (number of hours etc..)
Items starting with 2000, 3000 and 4000 refer to amounts (in principle part of the gross salary, subject to deductions or other)
Items starting with 5000 are for social security contributions
Items starting with 6000 refer to deductions and refunds
Items starting with 7000 are for amounts not subject to social security contributions
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Items starting with 9000 are for other items (provisions, statistics, etc...)
It should be noted that you can create as many items as necessary (up to 9'999) by clicking on the Add button. Only a user equivalent to admin has the right to create, delete or modify items.
It is always better to keep a logical order (the amounts submitted to something before the fields that are to be calculated on it).
Quantity items should be placed before other items because they will usually be linked to other items that will be calculated on them.
If you create new items, it is always a good idea to place them in the similar items area.