Thanks for coming to help. No, we can't say why we called – it's classified

On Call Register readers know the secret of tech support is that it's often made harder than necessary by the very customers who require it. Which is why each Friday we offer a fresh episode of On Call, our reader-contributed tales of icky incidents and hidden horrors that we hope create a chance to share misery in company.

This week, meet a reader we'll Regomize as "Tristin" who told us he once did field service for a "then-famous line of desktop calculators and their peripherals."

Tristin was based in Philadelphia, but in one glorious summer week the calc-maker's Washington DC office was short-handed so he was sent to the capital.

"Many of the customers were US government agencies of varying spookiness," he told On Call. And each had its own security measures before a techie was allowed in.

The service call in this tale involved an agency at which Tristin was "escorted through a huge steel double door." A member of the armed forces – bearing actual arms – stood at each side of this imposing portal.

Once Tristin entered, a rotating red beacon turned on so that everyone in the facility knew that a civilian who lacked security clearance was present.

For everyone's protection, Tristin was therefore shown into a curtained-off cubicle with a big world map on the wall.

"It was not unlike the then-current spy comedy Get Smart," Tristin wrote.

Make that "timeless spy comedy that helped to define On Call's childhood and writing style" please, Tristin.

But we digress. Sorry about that, Chief – missed holding the narrative together by that much.

Once within the cubicle, Tristin was told the agency used his employer's calculators to work out property boundaries, but was getting intermittent errors.

"Can you show me any examples?" Tristin asked.

"No" was the answer.

"Do you have an unclassified test data set which will show me the problem?"

Again, no.

With neither an example of the problem nor data to work from, Tristin said all he could do was run diagnostic tools.

"Will that change any data in memory?" the customer/spook asked.

Tristin admitted he would have to mess with memory.

"No, you can’t do that," was the response.

As Tristin pondered what to do next, he gazed upon the big map on the cubicle wall.

It depicted land masses as blank spaces, but included fabulous detail for ocean floors. Pinned to the map were a couple of what looked like infrared satellite photos of red streaks across the ocean.

Tristin guessed they were traces of exhaust water from nuclear submarines that the agency was tracking.

Could they enemy submarines? That was quite a prospect.

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With that idea in mind, Tristin suggested creating a dataset that omitted land areas so he could test the calculators' accuracy.

To illustrate his point, he joked: "The software won't care about a Russian sub in downtown Dallas."

"How did you know?" came the angry reply, followed by the odd admission that "The [REDACTED] are only interested in thirty feet or so below the surface."

Tristin's suggestion was rejected by a by-then visibly upset customer, who quickly showed him the door.

The problem was not resolved that day, and Tristin is unsure if it was fixed on any other.

But much later he was asked to consider a similar problem at a lens-grinding operation.

On that job he learned that "the calculator model in question had a problem with trigonometric functions of very small angles. On a typical land survey, such small angles seldom occur, and any error would have been smaller than the inevitable errors in the original physical measurements."

But on an oceanic scale, "the error could have been tens of miles …"

Have you found a small error with big impact? Or struggled to serve a classified client? Share your stories by clicking here to send On Call an email. We can be trusted with [REDACTED] material and the On Call mailbag is a hungry beast. ®