  This note introduces a new Bayesian control chart to compare two processes by
monitoring the ratio of their percentiles under Weibull assumption. Both
in-control and out-of-control parameters are supposed unknown. The chart
analyses the sampling data directly, instead of transforming them in order to
comply with the usual normality assumption, as most charts do. The chart uses
the whole accumulated knowledge, resulting from the current and all the past
samples, to monitor the current value of the ratio. Two real applications in
the wood industry and in the concrete industry give a first picture of the
features of the chart.
