see links.htm

top.js var qs = unescape(document.location.search)

qs is processed in getMolToLoad() in top.js including:

bu=  bmNumber, URLHasBU=true

aunonh=  auNonHCount

aubb= auBBCount

bu2auquotient =    bu2AU

The above are used after a dotPDB file containing REMARK 350 is loaded, in order to offer
BU1. See notes.htm#dotpdb (Filenames containing .pdb)