Capital Allowances Calculator - Balancing Charges are not displayed for Pooled Assets

Our Capital Allowances Calculator does not display a balancing charge when the Additions and Written Down Value brought forward from the pool exceeds the value of the Disposals.  We have had a number of queries from customers so our developers have produced the following guidance:

Capital Allowances and Balancing Charges

For a pooled asset the Brought forward amounts and the Additions are added to the pool and any disposals are subtracted from the pool after that. If the disposals are greater than the amount in the pool (BBF and ADDITIONS) then a balancing charge is made.

HMRC's Help Sheet  (HS252) for Capital Allowances and Balancing charges (See Page 7/8 for disposals) references the process.

'The procedure for computing the amount of the writing down allowance for each pool is as follows: 
(a) The written down value of the pool at the end of the previous chargeable period is brought forward
(b) The cost of any relevant P&M acquired (not subject to FYA or AIA) is added to the pool.
(c) For Pool items disposed of a disposal value is subtracted from the pool
(d) Available WDA is then calculated.
(e) WDA is subtracted from the pool to give a carry forward amount for the next chargeable period.

Balancing Allowances & Charges: 
'If the disposal value for the chargeable period exceeds the balance of expenditure in the pool before disposals are deducted the WDV of the pool is set to zero and a balancing charge is made which is equal to the amount of the excess.'