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We don't know why it's there, we don't know what it does – all we know is that the button makes everything OK again

It must be working, look at the LED

On Call An On Call reminder this week that all must worship the mystery beige box with the single baleful LED eye, no matter what one thinks it is used for.

Our tale comes from a reader Regomised as "Mike", an on-site engineer. Mike spent the late 20th century on the road, coming to the rescue of customers up and down Britain.

His story takes place in the 1980s, a decade that began with the debut of the Rubik's Cube and ended with the arrival of the World Wide Web.

Users had yet to learn the delights of seeking solutions to their problems via myriad ad-slinging search engines. Instead, Mike was called upon to deal with their complaints.

"I worked for a company supplying CAD systems," he told us. "These systems generally had some kind of 2D plotter for output, usually pen-based, but occasionally early inkjet technology or even a kind of wet electrostatic system."

"Which still gives me nightmares," he added.

The issue at hand concerned a mighty A1 pen plotter manufactured by Calcomp. Calcomp, for the uninitiated, was all about the plotter (besides other peripherals) and dominated the market in the latter part of the 20th century. It remained a thing right up until end of the 1990s before shutting up shop, although the name continues to live on.

The plotter in question was misbehaving: "It would occasionally refuse to work although there were plots in the queue," explained Mike. "I had a look, tested it and initially found no problem."

It was connected via a serial port. Sometimes a reset of either the plotter or computer was needed ("a good old DEC VAX 11/750") to restore the device to life.

Or sometimes a jab of a button on the formatter under the floor.

The what?

Mike had never heard of such a device, but the drawing team insisted it was there. A floor tile was lifted and, sure enough, nestled among the cables was a beige box with a Calcomp logo, red LED, and a single "Reset" button. Prodding the button caused the LED to flash and then go steady.

Mike poked around the rat's nest, but found nothing obvious amiss. He decided instead to check for bad cables.

"I traced the cable from the serial port on the VAX, through a patch panel, under the floor and up to the plotter, completely avoiding the magical beige box."

The suddenly redundant formatter merely glared back at him, its single red LED glowing in defiance.

"I had, and still have, no idea what that box did," he admitted, "apart from giving a sense of satisfaction and a powerful placebo effect."

Our money is on a no-longer-needed bit of kit that an engineer could not be bothered to remove. Or maybe, just maybe, a box to delay the inevitable callout just long enough for the shift to change.

What do you think? Let us know in the comments below and share your own experience with mysterious devices that are at once critical and utterly pointless with an email to On Call. ®

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