What wrong with this change handlers coding?

I'm currently working on a script that can read rotation angle of an object in real-time.

this is the code i used at this moment:

a=$cylinder01
fs= createfile "C:\\Users\\User\\Desktop\\source code5.txt"
when transform a changes do
(
in coordsys parent format "rotation-y cylinder 01 = %\n" a.rotation.y_rotation to: fs

)

and the result is as followed when i rotate the object:

rotation-y cylinder 01 = 27.9907
rotation-y cylinder 01 = 26.6364
rotation-y cylinder 01 = 27.9907
rotation-y cylinder 01 = -4.65485
rotation-y cylinder 01 = 27.9907
rotation-y cylinder 01 = -14.9164
rotation-y cylinder 01 = 27.9907
rotation-y cylinder 01 = -15.7972
rotation-y cylinder 01 = 27.9907
rotation-y cylinder 01 = -16.678
rotation-y cylinder 01 = 27.9907
rotation-y cylinder 01 = -17.5588
rotation-y cylinder 01 = 27.9907
rotation-y cylinder 01 = -19.3535
rotation-y cylinder 01 = 27.9907
rotation-y cylinder 01 = -20.6747
rotation-y cylinder 01 = 27.9907

The problem of this script is that it repeated the first angle it recorded as well. In this case, the error is the angle 27.9907, as u can see, it repeated every 2 lines.
Anyone have ideas on how to solve this bug?
i had troubleshooting for few days and i still dont know what's the problem with my code.