# Economic Interpretation of the Fair Forward ZCB Price

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The fair forward ZCB price is given as $$P_{tTS}=\frac{P_{tS}}{P_{tT}}$$ and there's a bullet point in the slides saying "economically, the bond forward price allows one (at $$t$$) to lock into a price for $$P_{TS}$$ (at $$T$$)".
The ZCB forward is a contract which allows one to lock into a price at time $$t$$ for the bond at time $$T$$. We can see this in the formula for the fair forward price. The fair forward price is the price one will pay for $$P_{TS}$$ at $$T$$, however it can be calculated at time $$t$$ since both $$P_{tT}$$  and $$P_{tS}$$ are measurable at time $$t$$. One therefore 'locks in' to this future price that one will pay for the bond by agreeing at time $$t$$ to pay $$P_{tTS}$$ for the bond at time $$T$$.