Complex sentence: Increased pressure will cause the two tines of the nib to separate slightly, allowing more ink to flow onto the page, whereas a lighter grip will allow the tines to remain close together and produce a thinner line.
Split into simpler sentences: Increased pressure will cause the two tines of the nib to separate slightly, allowing more ink to flow onto the page. On the other hand, a lighter grip will allow the tines to remain close together and produce a thinner line.