Double Interpolation Calculator
Software Application for the BlackBerry

This was originally conceived for use with aircraft performance tables in tabular format (e.g. Cessna), although the calculation - a generic double linear interpolation - is not unique to aviation or any other context.  It can also be used for a simple single interpolation.  It is a spreadsheet-style table which automatically calculates the result (and intermediate results) when the requisite inputs are entered.

You could think of double interpolation as adding a "virtual" row and column to a tabular lookup table. It is most simply explained by example:  Say you want to look up a 2nd segment climb gradient and your aircraft weighs 19,885 lbs.  You might only have performance data for 20,000lbs and 19,500 lbs, arranged in columns in the performance tables.  The temperature might be 21C, but you only have data for 20 and 25, in rows.

You enter the 3 weights and 3 temperatures mentioned above into the interpolation calculator, plus 4 climb gradient values from the table (shown below).  The result (3.39) is calculated and displayed in the center cell.  Note that the 4 intermediate results - each a single interpolation - are calculated automatically.