I have often joked about using "The Palmer Eyeball Algorithm" to fit a line or curve through some data points. It looks as if I do an okay job of eyeballing things, but there are others who are much better.
My average scores on this test were generally below 4.0 but were never below 3.0 (low is good), placing my scores roughly in the upper quartile of the distribution of those who take it.
Note: Each time you take the test, you make three runs through the test items. It takes maybe 5 - 10 minutes.
P.S., I know I'd have scored higher with a larger screen and a mouse instead of my puny near-netbook Toshiba and glidepad.
P.P.S. The first time I took the test, I was riding on a train. Understandably, the scores were very high.