The actual numbers (which are on the site I linked to, I believe, http://steroids-and-baseball.com/ ) show that the jump occurred somewhere mid '93 to 94.Can't find the numbers there, but from THT, HR% rates by season: 1988 2.7% 1989 2.6% 1990 2.8% 1991 2.9% 1992 2.5% 1993 3.1% 1994 3.7% 1994 3.7% 1995 3.6% 1996 3.9% 1997 3.7% 1998 3.7% The second graph is just the years lined up side by side, with the discontinuity edited out. No steady increase in power numbers (as if, more and more guys started using steroids), just one massive jump in a 1 year period. Here is an article on the CT scans of balls from Aaron's era and Bond's era. I'm still not getting it. I look at the first graph in your post labled as "Power Factor". If you count the hash marks on the bottom for years, in 1992 the rate is 1.48. In 1994 it's 1.57. If it was a one year jump it would stop at 1993, but it doesn't. The spike continues in 1994. Even the numbers in your post above support that. It goes up .6% in both 1993 and 1994. I also still don't understand the "adjusted" numbers in the splice graph. Like I said the "non-spliced" graph shows 1.48 in 1992 and the spliced graph shows 1.34 in 1992. How were the numbers "adjusted"? My assumption would be that it's basically subtracting the total "spike movement", which apears to be .09 (1.57-1.48), but instead of subtracting .09, it's subtracting .14.