Item base qunatity Keeps changing

I created an item withs sales and purchaes price, and qunatity of 1.  

i noticed after few invoices or incomes, the number changes all over, 0, -5, 3, and so forth, and i have to go in and re-edit it.

Thank you

ok. i see.  what this one refers to .. it is more of a stock mgmt.  

In this case, if there is no stock as these are back to back order. do i then just insert 999 in order to show that the stock is always there? and top it up when it is down to zero. ??

Yeah the inventory doesn't seem to work well. If you make an invoice and save it, then delete it later, the quantity does not go up again put back the items from the deleted invoice. This might be a feature to keep you from returning supposed 'used' stock to the 'new' inventory, but it seems like a glitch to me. If you aren't really tracking the inventory, then yeah you can just put a high quantity.