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 point data x1,y1 & x2,y2. Then type in an x or y value in the test fields, leaving the other field blank, and press calculate. The other field will be calculated. Press calculate again to clear the test numbers ready for the next.