Hi, This is my first post to the list, I've been using mason for a few weeks now. I'm using the Sequence class but have found the steps array inflexible in terms of adding new Steppables during execution. I've implemented an ExpandableSequence which uses an arrayList rather than an array. I was wondering if something already exists for this? I might use RandomSequence at some point, which would mean re-implementing RandomSequence to extend ExpandableSequence. Thanks, -- Mike This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.