  Comparisons of lattice-QCD calculations of semileptonic form factors with
experimental measurements often display two sets of points, one each for
lattice QCD and experiment. Here we propose to display the output of a
lattice-QCD analysis as a curve and error band. This is justified, because
lattice-QCD results rely in part on fitting, both for the chiral extrapolation
and to extend lattice-QCD data over the full physically allowed kinematic
domain. To display an error band, correlations in the fit parameters must be
taken into account. For the statistical error, the correlation comes from the
fit. To illustrate how to address correlations in the systematic errors, we use
the Becirevic-Kaidalov parametrization of the D -> pi l nu and D -> K l nu form
factors, and a analyticity-based fit for the B -> pi l nu form factor f_+.
