Hi KimberleyT ,
Thank you for your message.
I'm trying to respond you why the plugin is showing 14 instead of 10 (please, keep in mind I don't know the Price Measurement Calculator plugin and we don't support third party plugins).
ATUM allows you to use decimals in stock qty and when you sell a product with decimal quantities it stores this quantity in the _qty field of the order's line item. In fact, from my point of view and without knowing more about how you use the other plugin, with ATUM you would have enough, as people can buy products in decimal quantities.
As far as I can see, your plugin is storing the weight quantity you sell in another field and it's setting the qty to 1 element sold (so Stock Central shows in your site the number of sales). Please note this can change as the plugin allow users to buy more than one product of x.x weight.
I don't know where your plugin is storing the weight you sold, but to modify the quantities Stock Central shows, you can use the filter 'atum/stock_central_list/column_sold_last_ndays'. A developer could use this filter to change the quantities shown.
Hope this helps,