Interpolate2D
Function 
Interpolate2D(x, y, array)

Interpolate2D is included by default in each file as part of the Math library.
See also:
Use
The Interpolate2D() function returns an interpolated result from an "x" value, a "y" value, and a range.
The first input is the row/"x" lookup value, the second input is the column/"y" lookup value, and the third input is an array or range. The top row of the range is treated as the lookup row, and the leftmost column of the range is treated as the lookup column.
Interpolate2D() works with units. If the units for the lookup values are different than (but compatible with) the units of the lookup row or column respectively, Blockpad will automatically convert the units to find the right value.
Examples
Interpolate2D(2.5, 5.5, [ " ", 1, 2, 3; 4, 10, 20, 30; 6, 100, 200, 300]) = 193.75
Interpolate2D(3.1, 17, $D$3:$J$10) = 82.45
Example with units