The difference between the interpolation method and the extrapolation method, the causal method and the intuitive method, is that the interpolation method predicts within the range of the sample data and is more accurate than the extrapolation method. Interpolation method: refers to deriving a value between known values ??based on a known series of values. The interpolation method assumes that there is a certain clear relationship between the values. It is not an accurate calculation method, but it can be used to estimate bonds. price and yield. There are three types of interpolation methods: linear interpolation, logarithmic interpolation and cubic interpolation. Extrapolation method: In layman's terms, it is a good approximate calculation method. For the low-precision approximate value that has been obtained, as long as you perform the simplest four arithmetic operations a few times, you can immediately obtain a high-precision approximate value. More simply , it is a method of processing low-precision approximation values ??to high-precision approximation values, referred to as finishing.