http://www.morphography.uk.vu/scaleobj.html

Link to an article on Poser scale. Some points to keep in mind while reading this is most of the change in scale was caused by outside companies/people at around the time of Poser 5. Prior to Poser 5 what the scale was really didn't matter as they were all static images with no dynamics. With Poser 5 came Dynamic Hair and Dynamic Cloth, both of which require a scale to determine the amount of movement. As one of the most basic things is gravity and gravity is calculated as 16*T^2, you have to have an idea of how much distance that is in PNU's. As Poser has set it internal measurement system to 1 PNU = ~103.2 inches that really is what ought to be used even though that makes most figures too tall.

Poser 5, 6, 7, 8, Poser Pro 9 (2012), 10 (2014), 11, 12, 13