TODO: swap x and y, since gnuplot binary docu seems to be wrong :-)
> The `binary matrix` format contains a two dimensional array of 32 bit IEEE
> float values plus an additional column and row of coordinate values. In the
> `using` specifier of a plot command, column 1 refers to the matrix row
> coordinate, column 2 refers to the matrix column coordinate, and column 3
> refers to the value stored in the array at those coordinates.
Does the row move fast or slow?
