Android app connected to weight machine for customised weights and printouts

We run a fabric distribution warehouse where we sell fabrics in their roll form and the fabric is sold in kgs, each roll weighs from 15kgs to 25kgs and has a cardboard of 200grams to 400grams in each of the rolls, when we weigh the rolls the gross weight of the rolls is displayed on the weight scale display and we manually reduce the cardboard weight after multiplying it to the total number of rolls to get the net weight. I need a app which will give me a printout of the weight kept on the machine with some simple calculation. The weight machine has a RS232 port to which the mobile can be connected via a adapter and a usb cable. 1. The item names, item codes and the cardboard weight of that item should be imported into the app from a excel file. 2. once the rolls are kept on the weight scale the weight of the rolls needs to be captured by the app via the serial port connection and the item name of that fabric will be selected from a drop down menu and number of rolls kept on the machine will be typed into the app, after which if we press on a button the net weight of the item must be calculated for which the formula is Net weight = ( Gross weight - ( number of rolls * cardboard weight of that item)) 3. after the net weight is calculated it gets reset and we weigh the next item. 4. After the weight of all the rolls is taken when we press on print, a barcode of the weight details along with the item code is to be printed. and or send the details via sms or whatsapp. All the details mentioned above is for one user and the data is stored on the same mobile phone. Phase 2 of this app would be having different users of this app and syncing these details with other user of the same app along with admin control. Other smaller details can be discussed later as the details mentioned above is my overall requirement.