the FORECAST function to calculate the linear interpolation,.In brief, the equation consists of 3 parts: =FORECAST( NewX,OFFSET( KnownY,MATCH( NewX, KnownX,1)-1,0,2), OFFSET( KnownX,MATCH( NewX, KnownX,1)-1,0,2)) The simple implementation is easiest to understand by dissecting from the outside and working in.
