The right hand of dog

20 Oct 2009
Posted by colby

Today, John Sircusa re-tweeted a matching set of links from Devin Sanera on the placement of the movement sensor underneath the Apple Magic Mouse and prior research on the placement of motion sensors of mice in general.

Jonathan Hedley writes in, Why are mouse sensors in the middle of the mouse?:

"In a GUI, the mouse controlling the cursor is the fundamental link between the user and the computer. A strong connection is created for the user when the mouse performs well. The emotional attachment created between operator and system is strongest when the system does precisely what the operator requests. Imprecise controls make the operator feel that they are not in control: and so there’s a compelling case to get the design of the mouse right."


"...[most important of all], was the location of the mouse ball."

Too, fucking, right. Possibly one of the biggest overlooked issues with human computer interfaces in the last 20 years.

I learned to type in the my 10th grade year of high school. At the end of that class, I could make about 20-25wpm, and I could do it by touch, thus, employable in the temporary worker industry.

Soon after, I started chatting online while taking the odd programming or medical office transcription job. By the time 1995 (~9 years later) arrived, I was typing at up to 80wpm, and gradually destroying the sheaths around the muscles and nerves in my wrists between generic keyboards and generic mice. Being sore after a 8-12 hour day of working is one thing, being unable to type the following day makes the baby jesus cry.


I embarked on a campaign to find a keyboard and mouse that felt the most comfortable to me and that is how I settled on a combination I've kept for the last 15 years. A large Kensington Expert Mouse trackball (see fig 1) and and a Kinesis Contoured keyboard (see fig.2)1. Won't. Look. Back.

The trackballs I use put the movement of the device right under my finger tips and it wasn't until reading Jonathan's post that I realized this was a major reason why I use trackballs in the first place.


This is another arrow in my quiver of points about why I chose trackballs over regular mice. When I first used the trackball in fig 1, the ball itself was very light, but, just happened to be exactly the size of a billiard ball. I would immediately replace the ball with a 1, 8 or 9 ball. This gave the ball inertia, and allowed me to flick it and brake with my finger tips as the cursor arrived where I needed it.

This rules out all of the smaller trackballs I've ever tried to use. They have much less inertia and seem flimsy and too lose under my danty finger tips.


Happily, Kensington produced a superior product in the next revision of their Expert Mouse Trackball (see fig 3). With the addition of the scroll ring (around the ball, like a very large mouse scroll wheel) and increasing the density (i.e. mass) of the ball—which is very important—as their change to the motion sensors requires a custom ball.
Kensington's move away from mechanical rollers also makes the trackball much easier to keep clean and operating smoothly. I pop the ball out once a week (just turn the base over and it falls right out) and 3 seconds to swipe dust off of the ruby-red contact points.

I'm hopeful that other manufacturers will pay attention to the detail of having the sensor of a mouse nearer the tips of the fingers instead of under the palm or offset in some other way that makes it cheaper to manufacturer.

1I currently have 4 kinesis keyboards, all of which still work, ranging in birthdates of 1995, 1997, 1998 and 2000. The first three still have large 5-pin DIN connectors, plugged into my computers via DIN<->PS/2<->USB dongles. Kinesis has even sent me two replacement keys for free when I asked politely via email. Favorite computer accessory during my lifetime so far and favorite computer parts manufacturer.