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Comment by siglesias | Hacker News Reader

I think it pays attention to the accelerometer.

EDIT: In fact, it does. See thread below.

Also, dip your finger into an inkwell. Then press really lightly on a piece of paper, then press really hard on a piece of paper. Note the difference.

No accelerometer needed -- flesh is fleshy and distorts under pressure.

How does that account for finger size though? Children might have a hard press of the same area as my light press. Hm, could be they look at the rate of change in the growth of the tap event...but this wouldn't provide information about mass. I think it's a no go.

We need a force here. They know how heavy the iPad is. They have an acceleration. There's a force.

The same thing happens with a real piano though: differing fingers impart different forces with the same perceived effort, yet we still manage.

I was thinking that too, but they said they use an accelerometer. http://embed.scribblelive.com/Embed/v5.aspx?Id=22452&Pag...

This is an interesting idea. If one wanted to attempt a mechanism like this in iOS, what APIs would be useful? I don't know UIGestureRecognizer & friends very well at all, but it looks like it wouldn't help when needing to measure contact-area at a given contact point. Any iOS programmers here that know?

A good capacitive screen can determine the diameter of the touchpoint as well as the center. It's translating finger squish into pressure. It might also be looking at rate of change of the diameter over time to figure velocity.

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