uh, interesting, no easy answer to that one then! Thanks everyone for having a go though!!
I use a Geko 301, I don’t think that’s barometric (or is it? 😳 must check instruction manual…)
I did wonder whether there was something like the step effect druidh mentioned going on, but it seems that this isn’t likely?
Think I’ll go and have that cup of tea now (barney :wink:) and read your scientific explanations again!