  Jet precession can reveal the presence of binary systems of supermassive
black holes. The ability to accurately measure the parameters of jet precession
from radio-loud AGN is important for constraining the binary supermassive black
hole population, which are expected as a result of hierarchical galaxy
evolution. The age, morphology, and orientation along the line of sight of a
given source often result in uncertainties regarding jet path. This paper
presents a new approach for efficient determination of precession parameters
using a 2D MCMC curve-fitting algorithm which provides us a full posterior
probability distribution on the fitted parameters. Applying the method to
Cygnus A, we find evidence for previous suggestions that the source is
precessing. Interpreted in the context of binary black holes leads to a
constraint of parsec scale and likely sub-parsec orbital separation for the
putative supermassive binary.
