help with punctuation

[snkhaderi]

Which one of these is correct?

When the taper is zero the cilium has a uniform width, and when the taper is unity the cilium is triangular.
or
When the taper is zero, the cilium has a uniform width; and when the taper is unity, the cilium is triangular.

[Josef]

Both are possible, though there is no real need for a comma or a semi-colon so I personally would prefer:

When the taper is zero the cilium has a uniform width and when the taper is unity the cilium is triangular.