## 2018-01-22

### Facebook's New Unit of Time

Thesis: People who think every unit needs to be a power of 10 don't understand the importance of proper divisors.

Case study: Engineers at Facebook just invented a new unit for synchronizing video frames, called a "Flick", which -- to avoid rounding errors with floating-point math -- needs to be evenly divisible into any of the common video frequencies: 24hz, 25hz, 30hz, 48hz, 50hz, 60hz, 90hz, 100hz, or 120hz. And also multiples of those by 1,000. And also common audio sampling rates like: 8kHz, 16kHz, 22.05kHz, 24kHz, 32kHz, 44.1kHz, 48kHz, 88.2kHz, 96kHz, and 192kHz. Since the least common multiple (LCM) of all those numbers is 705,600,000 (see: Wolfram Alphalink) the "Flick" is therefore defined as 1/705600000 of a second.

## 2018-01-01

### Abstract

Do Scantron machines still require that the forms be filled out in pencil? You'll find many sites online that claim the answer to be "no", that was only truly a requirement some decades ago, and that one should feel free today to use any dark pen ink (example). However, with a colleague at my college I've recently tested this (December, 2017) on two different recent models of Scantron machines, and found that black ink is entirely not seen by either machine (all such answers scored as if blank/incorrect). So from the evidence at hand, the answer seems to be "Yes, Scantrons still require a pencil".

### Methodology

A standard Scantron answer sheet was filled out in pencil, with three questions marked. A student response form was filled out using a black felt-tip PaperMate Flair pen (link), with two questions marked correctly and one answer incorrectly. See forms below.

 Scantron forms; sample student response in black ink on the right.

These were run through two separate machines available at our college: a Scantron 888P+ and a Scantron Score. Both systems are identified as using OMR (Optical Mark Recognition), which several online sites claim should work identically for pencil and ink. I've been unable to find exact dates of production, but the Scantron Score is a newer model. The 888P+ has been installed at our college for at least 12 years; the Score was installed more recently, I think some time after 2010. Both models tested are shown below.

 Scantron 888P+

 Scantron Score

### Findings

On both Scantron machines, the sample student form in ink was marked with all submitted answers wrong, the same as if every entry was blank. See the image of the forms above, with the sample response for graded on the right. Every question has a letter to the right, indicating correction of an incorrect student response; the total score in the bottom-right is 000 (zero) for both models. (This form is double-marked after being run through the two machines; 888P+ markings are in red, while Score markings are black.)

### Conclusions

Scantron OMR machines, even fairly modern ones in the last few years (as of 2017), fail to recognize marks with blank ink all of the times we tested it, across two different models. Instructors should continue insisting that students bring pencils to tests graded with Scantron machines, and make sure to not advise students that ink pens will work the same way.