Strange Order on Calculation Field

Hi,

I'm having difficulty with ordering on a calculated field, the order
is just not doing what I expect. I'll post the query here, it is a
distance calculation based on lat and lng so it quite complex

SELECT * , (
ACS( LEAST( 1, CS( 0.898348891269513 ) * CS( -
0.00293599286770486 ) * CS( RADIANS( stations.lat ) ) * CS( RADIANS
( stations.lng ) ) + CS( 0.898348891269513 ) * SIN( -
0.00293599286770486 ) * CS( RADIANS( stations.lat ) ) * SIN( RADIANS
( stations.lng ) ) + SIN( 0.898348891269513 ) * SIN( RADIANS
( stations.lat ) ) ) ) * 3963.19
) AS distance
FRM stations
RDER BY `distance` ASC
LIMIT 0 , 30

So basically distance is calculated then I just want to order on
this, however this is what I get out

distance
9.6201
5.1337
12.508
3.5312
2.3165

So I'm confused, what strange kind of ordering is that?

Any help much appreciated,