xmlns:atom="http://www.w3.org/2005/Atom"
The residue of qualifying expenditure at any time is—
QE + B - A
where—
QE is the amount of qualifying expenditure,
B is the total amount of balancing charges previously made under this Part in respect of the expenditure, and
A is the total amount of any allowances (including balancing allowances) previously made under this Part in respect of that expenditure (whether to the same or to different persons).