Of all the ratios associated with the just sixth, the one likely to be the most consonant is 8/5.  The signal for a just sixth that is off by 4.32 cents. It is best viewed using markup such as used on the page c:User:Guy vandegrift/Musical intervals (tritone, fifth, minor sixth). Part of a collection of three images: File:Beat pattern for tritone.svg, file:Beat pattern for fifth.svg, and File:Beat pattern for minor sixth.svg.
Own work
Guy vandegrift