>But SI is already "prejudiced against prefixes that aren't a power of >1000". There are 20 SI prefixes. A full 16 of them are powers of 1000; >only 4 are not. If the in-between prefixes are so mightily useful and >so darned convenient, why don't we have prefixes for ALL the powers of >ten (see my list below)? Why do so many have no prefix?
There are very good reasons for this. 1. The convenience of being able to use a prefix so that the number involved falls into a 'familiar' range (somewhere between 0 and 100) is more prevalent around the base unit. For example, the difference in perception between 255 and 2500 is bigger than that between 20 200 333 & 202 003 330, even though both differ by an order of magnitude (either of the second pair seem big, so being able to reduce a 9 digit number to an 8 digit number by a suitable prefix is not as helpful as being able to reduce a 4 digit number to 3). 2. The base unit sizes are chosen so that they are practical for everyday use. The meter, kilogram & liter are all quantities that are easy to envisage and which ordinary people are likely to come across. Thus most people rarely need to deal with quantities that fall outside the milli- or kilo- range. So the reason we have power-of-ten prefixes close to the base unit is because (a) that is where most people operate and (b) that is where the convenience of being able to use prefixes to make the number manageable is most felt. Outside that range, power-of-ten prefixes aren't much more useful than power-of-1000 prefixes, so creating them would only make the system more complicated by giving us too many prefixes to remember. So it's not prejudice, just good basic design and power-of-10 prefixes are an essential part of it. ------------------------------------------------------------------- Tom Wade | EMail: tee dot wade at eurokom dot ie EuroKom | X400: g=tom;s=wade;o=eurokom;p=eurokom; Unit A2 | a=eirmail400;c=ie Nutgrove Office Park | Tel: +353 (1) 296-9696 Rathfarnham | Fax: +353 (1) 296-9697 Dublin 14 | Disclaimer: This is not a disclaimer Ireland | Tip: "Friends don't let friends do Unix !"
