VR’s success as an industry is closely tied to a key leading indicator: headset sales. That metric has grown at a slower than expected pace in 2017, and has a ways to go. We’ve pegged the current installed base around 17 million units, and the target for industry health is 100 million.

But what do current sales tell us about how headset penetration is trending? And what can we expect in 2018 and beyond? It depends on whom you ask. When looking at annual headset sales (different than an installed base figure) there’s a variance in projections from research firms.

Activate projects that annual sales of VR headsets will be around 1.8 percent of the global population by 2021. That’s about 100 million units sold per year (mostly mobile VR). At that pace of annual sales, the global market would reach a 100 million installed base around 2020.

Meanwhile, BI Intelligence projects far fewer global VR headset shipments. It’s comparative 2021 unit sales prediction is 43 million (mostly mobile VR). This scenario creates a longer time horizon to VR ubiquity, with that 100 million installed base being reached around 2022.

Lastly, IDC lands somewhere between Activate and BI Intelligence, projecting 67 million VR headsets sold annually by 2021 (chart below). This could be the “goldilocks” zone, somewhere between the two extremes above, and is still a healthy rise from 9.2 million headset sales in 2016.

Source: IDC

ARtillry is in fact more bearish than all of the above figures, projecting 2021 VR headset sales around 40 million units. In fairness to the above projections, they were made at various points over the past year and we now have a more recent and accurate picture of VR sales to extrapolate.

ARtillry’s AR & VR forecast will include these unit projections as well as revenue forecasting accross sub-segments of the AR & VR spectrum. That forecast will stand as ARtillry’s November Intelligence Briefing and will be published on Thursday. Stay tuned for more.

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Disclosure: ARtillry has no financial stake in the companies mentioned in this post, nor received payment for its production. Disclosure and ethics policy can be seen here.

Header Image Credit: Fortune