+# some constants to facilitate changes
+# maybe we display charge per petabyte in the future?
+use constant KB => 1024;
+use constant MB => KB * 1024;
+use constant GB => MB * 1024;
+use constant BU => GB; # base unit
+use constant BS => 'gigabyte'; # BU spelled out
+use constant BA => 'gig'; # BU abbreviation
+