We determine the relationship between the multiplicities
of the zeros of certain rational functions defined on the
${\rm SL}_2(\mathbb C)$ and ${\rm PSL}_2(\mathbb C)$
character varieties of knot exteriors.
This leads to a formula for the Culler--Shalen seminorms
associated to small Seifert Dehn fillings of such manifolds. 2000 Mathematics Subject Classification: 57M05, 57M27, 57R65.