diff --git a/code/termspecs/termspec.fsd-pos-neg b/code/termspecs/termspec.fsd-pos-neg
new file mode 100644
index 0000000..c0be898
--- /dev/null
+++ b/code/termspecs/termspec.fsd-pos-neg
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+# fsd weighted (vn+sd) correlations
+
+[u, v, w, y]
+
+c (latex="c") = 1.0 - y
+
+fsd (latex="\Sigma_f'") = sqrt (sqr(ddx(c)) + sqr(ddy(c)) + sqr(ddz(c)))
+
+nx(latex="n_x") = - ddx(c) / fsd
+ny(latex="n_y") = - ddy(c) / fsd
+nz(latex="n_z") = - ddz(c) / fsd
+
+divn(latex="\nabla \cdot \vec{n}") = ddx(nx) + ddy(ny) + ddz(nz)
+
+divn_plus = $positive(divn)
+divn_minus = $negative(divn)
+
+avg { c, u, v, w, fsd, ddx_c, ddy_c, ddz_c }
+
+avg fsd { u, v, w, nx, ny, nz, divn, divn_plus, divn_minus }