One of the most enduring sayings in our sport was provided by legendary Alpha Male big-wave rider, Buzzy Trent: "Waves aren't measured in feet and inches, they're measured in increments of fear."

It's the kind've quote that's been bandied about for years because it echoes the supposed don't-give-a-damn sentiments of big wave riders. But its use-by date has passed; modern big wave surfers do give a damn and the waves they ride are measured in feet and inches - albeit incorrectly.

Last week Garrett MacNamara won the Billabong XXL biggest wave award for a 78-foot bomb ridden at Nazare, Portugal, last November. The same wave was subsequently entered into the Guinness World Records as the largest wave ever ridden. The good folk at Guinness accepted the entry and proclaimed it a new world record.

It's important to note the previous world record, which was held by Mike Parsons for a Cortez Bank monster that measured 77 feet high, just 1 foot – 30 centimetres – smaller than Garrett's.

When Garrett caught his wave the footage circled the world, broadcast across surf and mainstream media as a "90-foot wave." Non-surfers lapped it up, while many surfers arched their eyebrows sceptically. Anonymous punters in online forums began to call bullshit while surfers in the public realm were giving the sort of evasive answers more typical of politicians. "Whatever size it was you can't deny it was a big wave," was a standard non-answer when pressed on the height.

MacNamara has since said that he didn't call the wave 90 feet and the figure was courtesy of an overeager publicist. The Billabong XXL award and the Guinness World Record are another thing entirely.

The Billabong XXL Awards are the brainchild of Bill Sharp. Sharp conceived them in 1998 (as the K2 Big Wave Challenge) and has run them since 2001 as the XXL Awards. His rationale is to take the subjectivity, the increments of fear, out of big waves and measure them purely objectively. It sounds very simple yet measuring big waves – especially big waves that are breaking - is anything but.

In 1933 an officer on the USS Ramapo measured what was then the largest wave ever encountered – a 122-foot unbroken behemoth in the North Pacific. The height of the wave was measured by a method known as triangulation. The officer, standing on the ships deck, lined up the crest of the approaching wave with the ship's crow's nest while the stern was at the trough of the wave. Knowing the length of the ship and the height of the crows nest above sea level they calculated the wave height. The methodology was sound.

Large waves have been measured by other reputable means. An altimeter was used to discern the height between crest and trough of a huge wave in the North Atlantic, and in a famous case the crest of a wave hit the deck of a North Sea oil rig, its height above sea level known. Both methods were foolproof and free of subjectivity.

In contrast the XXL judges calculated Garrett's wave by measuring his shinbone, presumably because it is a fixed, upright length, then extrapolating the overall height from that first measurement. This is an awfully crude way to measure a wave and it's fraught with inaccuracy because small errors get multiplied into large ones.

Allow me a quick example...

If Garrett's shinbone was 40 cm in length (average length of a shinbone) then that means Garrett's wave was 59 'shinbones' high (40cm x 59 = 23.6 m = 78ft). Yet if the judges got the estimation of Garrett's shinbone wrong by just 1 cm – the width of a human fingernail – then they have an overall margin of error of 59 centimetres.

At this point it'd be timely to remind you that Mike Parsons wave was estimated to be 30 centimetres smaller than Garrett's. So an error of just 1 centimetre, when extrapolated using the XXL method, makes the difference between supposed world records. The same would happen regardless of what reference point was used: shinbone, torso, or height of the surfer crouching.

Footage of Garrett was taken from a few hundred metres away. It is patently impossible to measure any reference point exactly and that's not taking into account errors of parallax or assessing exactly where the bottom of the wave is. In short, the base measurements used in the XXL calculations are subjective and taint the whole exercise.

If you believe this is too complex then remember these calculations are required if you're gonna give anything an official record. And if you have followed it so far then you'll realise how farcical the whole big-wave measuring business has become.

After the world record was verified by Guinness Bill Sharp spoke to Associated Press. "You can't deny how big it was for that moment," he said of Garrett's wave. And he's partially right, I can't deny it was a big wave, yet what I can't accept is that it can be quantified in any objective way. For all the dubious math applied we may as well measure Garrett's wave in increments of fear.