[Closed] tangentCurve3D error

I tried to get the tangential angle of a spline, but it looks like get error near zero.
Does anyone know why?

global a = 1
for i = 1 to 10 do
(
	p = (0.1/a)
	v = normalize (tangentCurve3D $ 1 p)
	a *= 10
	print (p as string +": "+(atan (v.x/v.y)) as string)
)

--> results in maxscript listener
"0.1: -11.1053"
"0.01: -6.03873"
"0.001: -5.99718"
"0.0001: -5.99714"
"1e-005: -5.99543"
"1e-006: -6.03104"
"0.0: -5.972"
"0.0: -47.9985"
"0.0: -47.9985"
"0.0: -47.9985"