I understand you're point but the calculations I'm doing are well with in the internal mantissa and are straight forward equations.

Can you point out where my calculation is not within the internal mantissa? Excel holds 15 digits. What's wrong with mine?

If you simplified your initial equation to “=(-1/900000000)*900000000+1” you do indeed get 0.00.

That's the point. The equation done by hand correctly reduces to zero. But I am only giving a concrete example. Suppose A, B, C, D, E, and F are variables

=(((A-(B/C))-D)*E)+F

Then, in the situation when

A = 1

B = 1

C = 900000000

D = 1

E = 900000000

F = 1

the error occurs. It means that you cannot implicitly trust Excel for the correct answer.

This is why it’s important to understand how floating-point calculations work and ensure you’re using properly formatted equations.

I agree it's important to understand how floating point calculations work. Please show in my example where this is a floating point calculation error.

As you can see from the formulas, my equations are very straight forward and do not rely on pi.

Really? The number of triangles that you are summing (the rather bizarre value of 1000507) is dependent on Cell C21, which is the arcsin function.

Since Excel returns ASIN(1) = 1.570796327 (i.e., pi/2), Excel's value of pi is built into the very heart of your calculation.