Average Number Of Sausages Over Time Period

We sell products out of vending machines and once in every few days (time span between readings may be different every time) read data from the machines using flash drive. Each reading from all machines produces an Excel file:

Reading_Date | Machine_ID | Product_ID | Amount_sold
2008-04-08 | 1 | 1 | 26

The only date that we have is the day on which the data has been read and this tells how many sausages were sold from the date of last reading till the date of current reading (after each reading counters are set to zero).

The problem is to get average amount of product X sold from machine Y on every calendar day. For a total rookie like me it seems like creating another column that would divide the Amount_sold by the number of days between two consecutive readings and put this average amount for every calendar day between these two readings. May it be done this way? How? Another way? How? I would be very grateful if anyone could help me and explain the solution in an accessible way.