# Learn Excel Episode 184: Straight Line Estimate

One of the simplest ways of forecasting is to assume that the sales are increasing along a straight trendline. Excel offers a function to calculate a trendline, but it is one of the most bizarre functions. If you don't know the secret to using LINEST, it will try and describe a line with a single value, like "208". This is enough to confuse even the rocket scientists. Let MrExcel show you the simple (but non-intuitive) steps to entering an array formula. Episode 184 will show you how.