Algorithm for “nice” grid line intervals on a graph

Question

I need a reasonably smart algorithm to come up with \"nice\" grid lines for a graph (chart).

For example, assume a bar chart with values of 10, 30, 72 and 60. You k

Answer 1

Using a lot of inspiration from answers already availible here, here's my implementation in C. Note that there's some extendibility built into the ndex array.

float findNiceDelta(float maxvalue, int count)
{
    float step = maxvalue/count,
         order = powf(10, floorf(log10(step))),
         delta = (int)(step/order + 0.5);

    static float ndex[] = {1, 1.5, 2, 2.5, 5, 10};
    static int ndexLenght = sizeof(ndex)/sizeof(float);
    for(int i = ndexLenght - 2; i > 0; --i)
        if(delta > ndex[i]) return ndex[i + 1] * order;
    return delta*order;
}