Product quantity can be bound to different policies. The policy defines how the module behaves and how it manipulates the quantity of the product.
When a user enters the quantity, the ordered quantity can specify a number of items (pieces, packs, etc.) in a shopping cart.
When the user presses the "Add to Cart" button, the module adds a row to the order.
When the user adds more items of the same product, the module combines all specified quantities in the same row. It is a regular PrestaShop behavior.
The ordered quantity can specify a number of whole units (but not items), for example, meters.
When the user enters the quantity of 45 meters for the rope, the shopping card will contain one product (rope) with the specified length of 45 meters
and not 45 items of the rope as it would happen in the standard PrestaShop installation.
While using whole units, every time when the user presses the "Add to Cart" button, the module adds new row with the specified quantity to the shopping cart.
Note: you can override this behavior by choosing aggregate quantities option in "quantity mode".
The quantity can also specify the fractional units (quantity in decimal values), like kilogram or meter.
This is the mandatory behavior for the grocery or fabrics shops. While using fractional units, every time when the user presses the "Add to Cart" button,
the module adds new row with the specified quantity to the shopping cart.
Note: you can override this behavior by choosing aggregate quantities option in "quantity mode".