In practice, rather than to presume a hypothetical condition that needs be validated theoretically, it is sufficient to accept a real condition that exists and can be directly validated for practical purposes. This paper presents a practical approach to formulating the theoretical price of a zero-coupon bond without the hassle of a change of probability measure - the martingale representation. The aim is threefold: theoretically, for modeling one need not presume a risk-neutral world which is born out of abstraction; conceptually, the notion of a fair price can be formulated by a verifiable condition - the martingale property; and computationally, the valuation of derivatives can be simplified.