Capital of Islamic Banking Windows units can be estimated in two ways: (a) The calculation uses the proxy that proportionates the capital structure of the bank as a whole. This assumes that the unit and the parent company have the same quality of financial exposure. (b) The authority requires the parent company to have a detailed policy for allocating funds and to allow the unit to manage the funds more independently. Apart from the differences, the unit can still apply the same treatments on current surplus/(loss) from sale of fixed and long-term investments and profit equalisation reserve (PER) from distributable income set aside for shareholders, as well as any other funds contributed by owners.