Available for sale investment securities are initially recognized at fair value, including acquisition cost associated with the investment. Subsequent to initial recognition, they are measured at fair value and changes therein, other than impairment losses, are recognized in the income statement and presented in the fair value reserve in equity for available for sale investments. When an investment is derecognized, the gain or loss is reclassified to the statement of income. For securities where there is no quoted market price, a reasonable estimate of the fair value is determined by reference to the current market value of another instrument which is substantially the same, or is based on the expected cash flows or the underlying net asset base of the security.