Yes, simplesimon/rad - I might have been asking for trouble with the last remark but it wasn't mischievous, I was trying to drop a little hint in a similar way to the way ifor has constructed the puzzle (whilst keeping both possibilities in play - so, no spoiler as such).
I think it's a pity that we've only got the one thread this week, because it's quite ingenious how ifor has been true to the theme, with the bars requirement being the agent of change (there's a whiff of Schrodinger in this, if you ask me).