Can someone help me out with my first ZoHo Creator Database?

I created a database with a form to submit data on a date base. The data entry consists of 4 columns.

For example:

Date            Value1  Value2  Value3  Value4

01-01-2016      10         15         20        10

11-01-2016      20         20         30        50

I would like to calculate the difference in values on a daily base, based on the datevalues in the Date column.

Based on the example above the avarage daily value for Value1 is 1 ((20-10)/10))

How can I count the number of days between 2 Date values in the Date column?

Many thanks in advance.

Regards,

Wilco