h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Hi Jim

I'm researching an Entry about check digits. This has led me all over the place, but I'm particularly interested in those used on h2g2 at the moment. Traveller in Time and Gnomon have given me some helpful pointers, but I really need your assistance.

I understand if this subject may be 'trade secret' and if you don't want to divulge how they are constructed. Basically, the things I need to know are:

Where they are used, ie on Guide Entries
Where significantly they are not, ie on Researcher numbers
What principle they are based on, ie Modulo 10 and the remainder values employed
Why, if at all, the remainder values were specifically chosen
Why the check digits were necessary

As an aside, could you tell me why Researcher number U2 doesn't appear 'blue' as I have been discussing here: http://www.bbc.co.uk/dna/h2g2/brunel/T2541466#p29979769

Thanks!

The check digits are only used for GuideEntries. We decided to use them because we figured that people would occasionally write them down or read them out, and the check digits would allow us to catch errors and suggest corrections. We didn't do it anywhere else because we just didn't think it was worth it.

It's based on modulo 10 and the easiest way to calculate it is to add up all the other digits (the check digit is the last digit) and the check digit is the number you need to add to make the total end in 9. Another way to put it is the check digit is 9 - (sum of digits modulo 10).

U2 doesn't appear in blue because that confuses people talking about the band. Likewise, F1. There are a few other exceptions to the auto-linking feature.

I'm certain that U2 and F1 used to apear as links. I remember having a conversation about it.

U2 is Nobody, an inactive account.

And F1 is rather odd. It's a conversation forum, but it doesn't say what it's a converation forum for. And though there are only six converasations, there are two radio buttons. The second is blank. It just says: "There are no conversations on this subject yet. Click on 'New Conversation' to start one." Which is untrue.

TRiG.

> "I'm certain that U2 and F1 used to apear as links."

Yes, they used to ... and now they don't. There was also a conversation about what F1 was for but, since you don't remember it, perhaps you weren't in that one.

Do T-numbers appear as links these days? I'm sure they used to.

This lead me to a little confusion here: F2767103?thread=2673138&skip=40

TRiG.

I don't think T numbers have ever appeared as links (except when explicitly linked). They aren't really official (unless someone's changed the FAQ recently) and aren't guaranteed to work properly (there have been a few bugs with them, and I think there's still at least one unresolved issue with them). They were just put in as a quick shortcut which helps development.

T-numbers haven't auto-linked in the time I've been looking (end of 2002 onwards). I'd suspect they never did.

I have seen them linked, but maybe as Jim Lynn says, that was explicitly done (like <./>NamedEntries</.&gt, just as MP and RF pages can be made into links.

TRiG.