I seem to recall Hewlett-Packard used to make probably in the late 1980s, portable typewriter-like things with a keyboard and a roll, but instead of a printing head, a plotter capable of using four colour pens to "print" the letters typed on the keybo...

Michael Porter

@riley No idea, but I assume position information comes from the device with the screen as opposed to the Apple Pencil. So the map would have to be on a screen, unless you introduce more tech inside the Pencil. Maybe you could modify one of those “scanners in a stylus” devices?

You brought back another memory from my undergrad days - we didn’t have access to the really nice machines, so if we wanted to determine the area under a curve for a spectroscopic or chromatographic plot, we would photocopy the plot, physically (with scissors*) cut out the curve in question, weigh it to a few decimal places, and compare to the weight of a known area of paper. The precision of the cut, and the consistency of the paper added a couple more sources of uncertainty

*Young ‘uns don’t appreciate TRUE cutting and pasting these days

Riley S. Faelan

@MichaelPorter Yep, with a current Pencil, you'd need a positioning grid underneath the paper. But, AFAIU, it's not there to itself decide the position, but to provide a precision-shaped electic field grid for the Pencil to measure, since current MEMS accelerometers and gyroscopes aren't precise enough to decide absolute coordinates of the Pencil's tip just yet.

I believe Apple uses the same technique as Watcom's graphics pads, although I'm not sure if they're similar enough to be compatible with each other. In any case, Watcom's pads have usually had raised bevels, and Apple's pads come without such bevels, which makes those friendlier towards shoving the pad underneath a page in a bound book for a quick planimetric measurement.

Riley S. Faelan

@MichaelPorter If Newton had been more influential on the 20th century, perhaps fancy advanced calipers and slide rules would have had some sort of difractional grating mechanisms for multi-digit precision-reading, instead of the Vernier scales that don't really go further than three digits at the hand-sized tech.

Riley S. Faelan

@MichaelPorter Imagine numbers of each scale being lit up by a different light-guide, so you could switch over which scale's numbers shine brightly.

Michael Porter

@riley I own a Wacom tablet and an iPad, so you got me curious (links below, ff your’e interested).

It looks like the surface does all the work in detecting the pen and its position. The Wacom basic styluses have an LC circuit in them, tuned to a particular frequency (or range of frequencies, rather). I’m sure Apple uses a different frequency, but wouldn’t be surprised if the new crop of Wacom wannabes (that have arisen since the expiration of the relevant patents) use the same frequency as Wacom so as to take advantage of compatibility (sell pens to Wacom owners, sell tablets to people who have pens, etc. Total speculation on my part there, though.

More bells and whistles, in the form of accelerometers and gyroscopes you mentioned, require power, so the Pencil needs to be charged while my Wacom stylus does not.

My Wacom tablet does not have a raised bevel, so either device would be fine for laying a piece of paper on. Seeing the effect of that paper on the capacitance will have to wait until after I walk my dog

Links that helped me (not an endorsement, just the first ones I came across. If you know of better ones I’d love to have ‘em):
https://essentialpicks.com/how-apple-pencil-work/
https://essentialpicks.com/emr-stylus-how-wacom-pens-work/

Michael Porter

@riley Whoops, I almost replied with a rational comment

For the archives:
Pushing precision past 3 sig figs is probably unnecessary for most applications.

Riley S. Faelan

@MichaelPorter So, it's exactl the sort of unnecessary fanciness that Elves would do if Elves made slide rules.

Riley S. Faelan

@MichaelPorter Then, Apple's thing is probably not Wacom-compatible. The Pencil notably includes a small processor and does quite a bit of computation on board, although the main purpose of this computation is to track the Pencil's gyroscopic location and the tip's pressure, so fusing that data with location gathered on the panel's side would not be entirely out of the question. Still, I doubt Apple would have split it up like that.

Also, Pencil does not interact with the capacitive touch panel (other than by sensing the pressure and angle of its tip being pressed against the glass of the screen). It strictly requires another, further, layer of electronics to function. This is also convenient for reliably telling finger-touches apart from Pencil-touches, which typical Android devices with hacked-up capacitive styli just can't do.

Riley S. Faelan

@MichaelPorter Oh, btw, I'm pretty sure that the Wacom tablet has no problem at all with a single sheet of paper, for backwards compatibility reasons. Wacom's graphics tablets didn't exactly fall out of a coconut tree; instead, they developed from, and used to compete against, an older similar class of devices called 'digitisers', whose major use case was tracing pre-drawn drawings from paper into a computer.

Riley S. Faelan

@3rz Danke!