Return a non-negative float value indicating how much the amount of this
budget item should be multiplied by in order to get the budgeted amount for
the given period.
Bank ID: used or not according to country:
BEL Bank code
CAN Routing and transit number
CHE Clearing number
DEU Bankleitzah
ESP Entidad
FRA Banque
GBR Sort code
ITA ABI
NLD Not used (field contents ignored)
USA Routing and transit number