Scrolling text with variable pitch fonts

I just had a hard time learning how to implement a vertical scroll. The next thing i want to try is a horizontal scroll and i learnt that some fonts have a variable pitch. So what is the ideal way to scroll the text with variable pitch fonts, say when a SB_LINERIGHT msg is received?

Do I :
1) scroll the text by 1 tmAveCharWidth to the left?
or
2) scroll the text by 1 tmMaxCharWidth to the left?

On top of that:

- I was taught to find the client window height and divide by the (tmExternalLeading + tmHeight) for the vertical scroll. But how should i set the horizontal scroll nPage for the scrollInfo when there are variable pitch fonts?

Thanks