Touchable button

I'm creating a single screen 2D game and I want to create mobile touch controls for the player. I'd like an invisible slider/button that would give me the position of the current touch relative to the button's position. In other words, it should work like a horizontal slider that would be able to change it's position based on the user's finger location. I'm not interested in pointer down/pointer up events only, but I need to continuously check the position of the finger. I hope my description is clear enough. Please, help me, because it's my first Unity game and I'm struggling.

 

I ended up adding an empty game object with a RectTransform and then calculating the local click coordinates with the following equation:
localTouchPosition = touchPosition - transform.position
then I can use the local position to transform it further into a percentage position:
percentagePositionX = localPosition.x / rectTransform.rect.width
percentagePositionY = localPosition.y / rectTransform.rect.height