Visual acuity

I've read somewhere that with good vision you can resolve features on the scale of 500 arc seconds (0.1 degrees), or around 1/8 inch at 10 feet. But this is only true at the center of your field of view.

Then there's the issue of how fast your acuity drops off from the center of your field of view. Last October, Skip forwarded this to me, from a paper at

Visual acuity is the ability of the eye to resolve detail. The retina of eye can only focus on a very small portion of a computer screen, or anything for that matter, at any one time (Wickens 1992). This is because, at a distance greater than 2.5 degrees from the point of fixation, visual acuity decreases by half. Therefore, a circle of radius 2.5 degrees around the point of fixation is what the user can see clearly. In the GUI world, this is the Rule of 1.7 (Sarna 1994). At a normal viewing distance of 19 inches, 5 degrees translates into about 1.7 inches. Assuming a standard screen format, 1.7 inches is an area about 14 characters wide and about 7 lines high (Helander 1988). This is the amount of information that a user can take in at any one time, and it limits the effective size of icons, menus, dialogs boxes, etc. If users must constantly move their eyes across the screen to clearly focus, the GUI design is causing a lot of unnecessary and tiring eye movement.

According to studies cited by Jakob Nielsen, 300 dots-per-inch at typical reading distances may be a magic number for resolution — this is the resolution at which people can read as fast as reading old-fashioned typeset documents.

Web authentication with outbound call

is a new product that authenticates Internet users with a two-factor
technique that includes web interaction plus an automated outbound
telephone call to that user. During the call, the user must enter data
on the telephone keypad and have his or her voice data recorded.
Businesses can use this additional information to better authenticate
users and have a better audit trail.

Microkernel OS vs. monolithic OS

Andy Tanenbaum (author of the Minix OS) and Linus Torvalds (author of Linux) had this interesting debate on comp.os.minix in Jan & Feb of 1992.

Andy had a nice definition of things:

whole [monolithic] operating system is a single a.out file that runs in
'kernel mode.' This binary contains the process management, memory
management, file system and the rest. Examples of such systems are
UNIX, MS-DOS, VMS, MVS, OS/360, MULTICS, and many more.

In a
microkernel-based system, in which most of the OS runs as separate
processes, mostly outside the kernel. They communicate by message
passing. The kernel's job is to handle the message passing, interrupt
handling, low-level process management, and possibly the I/O. Examples
of this design are the RC4000, Amoeba, Chorus, Mach, and Windows/NT.

is micro-kernel and Linux is monolithic (at least as of 1992). It's a
very interesting discussion between two interesting guys.

brings up the issue of multithreading support in Linux vs. Minix. Andy
has a response that is funny until you realize what things were like
back in 1992:

When there is only one job active, the
normal case on a small PC, it [multithreading] buys you nothing and
adds complexity to the code.

Study: Few users reject cookies

A study by Web Side Story has found that only 7 out of 1000 Internet surfers reject or block cookies.

quote from Jason Catlett of the was amusing: "…
There's still the fact that when cookies are explained to [computer
users], they do not like them." I'm sure that statement is true given
the way Mr. Catlett probably explains cookies.

Browser cookies
are like sharp kitchen knives: most of the time they do a useful job,
but in the hands of the wrong person they can be use to harm others.
You may also be tempted to compare cookies to guns and the adage, "Guns
don't kill people, people kill people." But that comparison is too
extreme: improper use of guns has enormous consequence, unlike cookies.

the fact that this study shows only 7 out of 1000 block cookies seems
to say to me that the general public regards cookies in the same
category as knives, not guns.

Biometrics in hospitals

Another naive article about biometrics (5 Apr 2001) in hospitals to protect sensitive patient data. From MedcomSoft, a Canadian company.

How is this any better than a password? In fact, it's worse than a password for two reasons:

  1. If
    your password is "cracked", you can change it. On the other hand, if
    there's some kind of a bug in the software of the fingerprint reader
    such that they can capture the digitized image of your fingerprint,
    then your screwed. Hmm, actually that could work ten times. But then

  2. What about people with no fingers? What about people who loose fingers?

Sigh… Bruce Schneier has covered all this ground in his Crypto-Gram newsletter and his book, Secrets & Lies.