Harry, thanks. I have used one you wrote out this morning in another thread, in fact, and another which would only put the series number in with the title. In both cases, it will work for one or two books, and not for any others. I have tried it both with the kindle keyboard and the paperwhite.
I currently have these two installed
mobi:any device = {series:|| }{series_index:0>2s|| - }{title}
mobi:kindle2 = {series_index:0>2s} - {title}
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