[Hitchhiker 42]

Originally Posted by Ether

@Mark: Where did you get the accel formula for columns D and G.

Not sure. Must have been really tired . I did that over, and also added an error column to show the difference between Xa and the predicted X (Xm or Xe).
I set dt = 0.01 s and compared the errors at t = 1, 2, 4 s

For 1s:
Midpt error: 0.598
Euler error: 0.585

For 2s:
Midpt error: 2.834
Euler error: 2.748

For 4s:
Midpt error: 50.070
Euler error: 48.113

Seems that, at least for this function, the Euler method holds up better. Tomorrow, I'll try it with a function where the second derivative isn't always positive on the interval I'm testing.