A new documentation is available for Squash TM 2.0 and later versions, check it here
Five graph types exist:
Distribution (diagram), on which you can choose the axis.
Histogram, on which you can choose the x and the y axis.
Evolution, on which you can choose the x and the y axis.
Trends, on which you can choose the x and the y axis, as well as the data series.
Comparison, on which you can choose the x and the y axis, as well as the data series.