I wondered this too and asked the company. They said there isn't any mechanical or option difference...so I guess this is their way of saying its just the colors. Interestingly, on their website, when you go to the HJ113 page it actual says "HJ112" in the descriptive text.
Zue says: The difference between the HJ-112 & the HJ-113 is very slight. One is slimmer & longer, and the other is shorter & fatter. BUT .. only by 1/8" in either direction. The big difference, if you consider it so, is that the HJ-113 tells you the FAT GRMS. burned, as well as the CALORIES burned. You will see this displayed under the Calories Burned instead of the time displayed. The HJ-112 only displays the CALORIES burned, with the time underneath. The HJ-112 has an extra button on the face for reset. The HJ-113 eliminated the 4th button, but has built-in the reset within one of the 3 buttons. Hope that helps vs. confusion? Otherwise they are very similar.
I do not own a HJ-113 but the instruction manual is available on the company web site. http://www.omronhealthcare.com/product/manuals.asp There is a slight difference in size. HJ-113 is shorter and thicker. Color is different. HJ-113 has no reset button. It looks like there is no way to reset the current day's numbers to zero. You would have to wait for midnight. Maybe there is a model HJ-113 in Europe that is metric, but the manual I saw is not metric.
Yes, I've been using the HJ-112 for a few years, imagine that, the HJ-113 allows you to view the aerobic minutes associated with the aerobic steps of the pass 7 days. My HJ-112 does not, but I still can't justify that as a reason to upgrade.
I believe the main difference was difference in color and that the HJ-113 had a reset button. I bought it a few months ago and it had a reset button. It might have been since updated and the reset button removed which would make me happier. I accidentally reset mine a few times and messed up my steps for the day.