So, if using the unit factor then would do away with the attrbutes as they would well be confusing. If there are price differences for box sizes then could apply quantity discounts. The unit factor is located on the product info page when in the admn. There is also a minimum value which would just be wise to set at 50 as well.
ZC Installation/Maintenance Support <- Site
Contribution for contributions welcome...
So there isn't a solution?
There's always a solution...
Instead of using attributes, you can make some code changes and convert the quantity input field into a select menu (drop down) with your preset quantities. As mc12345678 already mentioned, you could adjust the price with qty discounts (in case 1000 pieces costs less than 5x200 pieces). You would also need to make sure to edit the qty input on shopping cart page, as well as any product listing pages (product_listing, products_new, specials etc).
There is a caveat with this method - if for any reason I want to purchase 3 separate packages (one for me, one for my wife and one for my grandma) and I want 100+100+50, the shopping cart will NOT separate it and you'll get an order for a single package of 250... The only way I can think of to keep it separated is using attributes. And with attributes, you're stuck with using SBA... Although, I don't see why you don't want to use that plugin - it's pretty good and stable, easy to install and simple to maintain...
Thank you for the help.
Agreed to the first, with yet-another caveat for the attributes-handling: Given that the "number of rounds" attribute is known, one could write a somewhat simple observer to check, upon order creation, whether such an attribute exists and to reduce the associated product's stock by the value specified in the attribute's value -- i.e. the attribute values for "Number of Rounds" are the (ahem) number of rounds: 50, 100, 200, etc.