Can't beat free.
I am incubating "low" this year, because I am have a lot of spider clutches and wanted to do an experiment. Incubator temps are set at 86, but egg temps are still hitting 88 and 89. Ambient temps outside the incubator are between 84 and 86, so I am getting some very interesting readings. At any rate, none of the eggs have been pipping before day 60. I trust that BCR's observations are also accurate. As to a chart, if you find one please post it. I have not found anything either.