[wdmmg-discuss] Number of digits for money amounts in dashboard etc

[David Jones]

Some of the money amounts displayed by the dashboard use 4 digits (EG  
"The Environment: £4894mn").  None use decimal points.

I think the display should use at most 3 digits.  And therefore a  
decimal point should be used.

So 4.89bn rather than 4894mn.

I note I'm not alone in thinking some of this: See http:// 
www.wheredoesmymoneygo.org/comments/dashboard/#comment-257

In fact, I think 4.89bn is a bit too cluttered, and 4.9bn would be  
better.  Besides, it's not like anyone believes more than the first  
digit or so, right?

So my rules for displaying an amount are:

- Choose whichever of million or billion (or presumably thousand,  
trillian, etc) makes the integer part, when rounded, 3 digits or fewer;
- if the integer part has 3 digits, just use that;
- otherwise (the integer part has 1 or 2 digits), add a decimal point  
and one digit after the decimal point.

So:

4.9bn
489mn
48.9mn
4.9mn

There is a corner case in the first part: 999,700,000 should be 1.0bn  
not 1000mn (hence the "when rounded" in the above rules).

The hover over balloon could easily display more detail if needed.

What do other people think?

drj