What happens if you use explicit type conversion and .Value instead of .Text, i.e.

Dim A As Double

A = CDbl(txtA.Value) * Math.Pi / 180

And then use A in the equation (and the same for R and E)?

What are the values of your text boxes when you perform the calculation? Also note that if "your calculator" is Windows, it performs 64-bit operations, not 32-bit, but without the original values, I can't measure the impact.

VB: PI = 3.14159265358979

Calc: PI = 3.1415926535897932384626433832795

(°v°)