I've been struggling mightily with the issue of how to convert BC dates to Gregorian equivalents. I think it turns out to be senselessly complicated. W3C (ISO 8601) dates, which aspire to be computable, include a zero year, which is equivalent to 1BC, but XSLT date-arithmetic stumbles over this with an error; meanwhile, various accounts of the proleptic Gregorian have it including a zero year or not including one. It's difficult to know what a conversion to proleptic Gregorian could mean in such a context. Nothing at that period seems to be accurate enough for the Julian/Gregorian difference (which is only a couple of days at that point) to be worth worrying about.

So what I've decided is this: for any negative Julian dates, I just add the little mouseover saying "This is a Julian date." I don't provide any suggestion of what its Gregorian equivalent might be.

This (and some appropriate error-trapping) means that TRIU2 is working again.