Calculate exchange differences correctly

In v2015 a euro invoice of €1038679 @ 0.725 shows a control account posting of £753042.46

In v2015 posting a payment for €1038679 @0.70 shows a control account posting of £727075.30

You would therefore expect the currency gain to be £753042.46-£727075.30= £25967.16

But it is not because the calculation the system makes is €1038679 / (1/0.7 to 6 d.p) i.e. 1038679 / 1.428571 = £727075.52

The currency gain is therefore £753042.46-£727075.52= £25966.94

The postings to the control account are therefore:-

£753042.46 Cr

£727075.30 Dr

£25966.94 Dr

Total £0.22

The same transaction posted with the same Euro rate in v2013 shows a control account posting of £753042.28

The same payment posted in v2013 results in a control account posting of £727075.30

And the same exchange difference of £25966.94

The postings to the control account are therefore:-

£753042.28 Cr

£727075.30 Dr

£25966.94 Dr

Total £0.04

So both versions are wrong in different ways. Although the differences are usually small they add up and make it practically impossible to reconcile the control account