At least once a year I get the problem: I've got two points on a line; I want to know zero crossings and other specific values. Every time I have to write down the equations and solve them...but no more. With this calculator I can now turn my brain off and let the PC do the thinking for me!

Quick summary: You have 2 sets of (x, y) points - that is enough data to define a line y = m*x + a; where m is the gradient and a is the y-axis crossing. By substituting the data and solving for m and a, any other point on the line is then easily calculated.

To use this calculator: type in the line data point x1, y1 & x2, y2. Then type in apoint you want to test, x or y, leaving the other blank, and press calculate. The other field will be calculated. Press calculate again to clear the test point ready for the next.