Interpolation guides

What is interpolation? Estimating values between known data points: the main methods, their formulas, and when each one is the right choice. How to interpolate steam tables Single and double interpolation in saturated and superheated steam tables, worked step by step with real table values. How to interpolate in Excel and Google Sheets Five ways to interpolate in a spreadsheet, from a one-line formula to a full table lookup, with formulas you can copy. Interpolation in Python Which function to use for linear, spline, polynomial and 2D grid interpolation in Python, and the gotchas in each. Choosing an interpolation method How accurate each method is, when it fails, and a simple decision guide for picking one. Newton forward and backward difference interpolation How to build a difference table, which formula to use, how many terms to keep, and two fully worked examples.