The SA specs quote +/- 0.4 dB which I though were pretty good. It turns out that my -1.5dB loss problem was not with the SA but with the 50 ohm coax cable... switching to a 'brand' name (though still made in China) brought things back to spec...actually within (-)0.25 dB of my NIST source. Good lesson here, at least for me :-)
Jerry NY2KW