Coronavirus: NZ COVID-19 Tracer app explained - how QR codes work

The Government launched its much-anticipated coronavirus contact tracing app on Wednesday, allowing New Zealanders to create a 'digital diary' of all the places they visit.

The app - called NZ COVID-19 Tracer - was released to mixed reviews, with some people unable to find it in their device's app store and others complaining of poor design.

But others have lauded its simplicity; after all, you just need to open up your app, hit the 'scan' box, then hold up your device's camera to the QR code. Users can also add their details and address to the app so contact tracers can get in touch with them.

But it appears the system is not simple for every Kiwi, judging by a surge of Google searches for 'QR code' in the lead-up to the app's release.

If this is you - and there's no shame - read on.

QR codes are like barcodes, but better

QR codes were invented in 1994 by Masahiro Hara, of Japanese tech company Denso Wave. They have become increasingly popular with businesses in recent years, in some cases displacing the standard barcode system.

QR codes are similar to barcodes in that they are altered in small ways to create an individualised code that is digitally scanned by a machine. However while barcodes can only be read left-to-right, QR codes operate across two axes - both horizontally and vertically.

This means QR codes can be individualised in far more ways, and reduces the chance of them being misread by a scanner.

They come in a fixed number of different sizes, known as 'versions', and each version has a different number of dots, known as 'modules'.

While its not known what version the Ministry of Health uses for its app, the medium-sized version has 15,000 different modules, which can be arranged in quintillions upon quintillions of different ways, according to computational knowledge engine WolframAlpha.

How the NZ COVID-19 Tracer app uses QR codes

The Ministry of Health uses QR codes to "encode information such as the name of the business and the location of the premises," it says.

Businesses or public-facing organisations with visitors or staff coming on-site can generate their own QR codes for each of their premises, as long as they have a New Zealand Business Number (NZBN).

This can be done through the Ministry of Business, Innovation and Employment's (MBIE's) Business Connect service.

"Each QR code poster contains a scannable code based on the business's NZBN and Global Location Number," the ministry's website reads. "QR code posters should be displayed where your staff and/or customers enter the premises."

What does a QR code look like?

The QR codes the app uses is in the shape of a square, with block patterns in black and white, surrounded by the distinctive yellow stripes seen on all the Government's COVID-19 messaging.

NZ COVID Tracer app QR code posters look like this: 

Coronavirus: NZ COVID-19 Tracer app explained - how QR codes work