Text scroller behaves oddly

hello everyone.
i want to make a slider bar to scroll a text using my own design.
first i followed and addapted the nice kirupa’s tutorial about slide bars to work vertically. i figure my main problem is with the formule that controls the movement of the text, but there are also other strange things, like the difference between the height of the text i see in the properties window and the same value shown in the control box i placed on the stage to check the variables… and once i release the mouse button, the slider will not slide to up and after some more tries it won’t slide at all.

while searching the forum to check if someone had asked that before, i saw a thread where someone mentioned it’s possible to edit the component. is it also possible to change the pictures used by the component? how can i do that?

the .fla file is attached. thanks in advance for any help