For virtual reality to be consistent and immersive, both tracking and headset displays must be calibrated to the highest precision. If aspects of these are incorrectly set up, the experience as a whole can massively suffer.

If you're an HTC Vive user, you might have noticed the subtle knob hidden at the bottom right of your headset. With almost no guidance from HTC, this knob is often left untouched by a majority of VR users. So you may be wondering – what exactly is the purpose of this knob?

What does that knob do?

Simply put the knob, referred to as the Interpupillary Distance or IPD knob, changes the spacing between the HTC Vive's two lenses. The optimal position of the headset's lenses hugely varies from person to person and if incorrectly configured, can lead to an inaccurate onscreen image.

This is due to the two separate screens that make up the HTC Vive's display, which render different images to produce a sense of scale. If the parting of these lenses if offset differently from your pupils, the resulting image will be somewhat distorted. This can include an imbalanced sense of scale and while discreet, can harm an otherwise immersive experience.

How do I correctly tweak my headset's lens spacing?

As previously mentioned, the IPD setting hugely varies between different users. This refers to the interpupillary distance, which is a measurement to indicate the distance between a person's pupils. This must align correctly with the headset for the best experience. In some situations, correctly tweaking the IPD is just as important as resizing the head straps.

Ensuring your HTC Vive's IPD is correctly configured is considered to be a crucial part of the set-up process, but in reality isn't easy to accurately set. Unless you have the tools and knowledge to correctly measure your interpupillary distance, only an optician or doctor can provide you with a precise value.

While there isn't an accurate method of measuring your exact IPD at home, a rough estimate can be obtained with a simple millimeter ruler. Here's how to personally measure your estimated IPD:

  1. Place a millimeter ruler against your brow
  2. By standing in front of a mirror or with the help of a friend, measure the distance between the center of your pupils.

With the estimated distance you've measured, apply this to your HTC Vive using the steps below.

  1. Open SteamVR
  2. Rotate the IPD knob located at the bottom right of the headset.
  3. An onscreen IPD pop-up will appear within SteamVR, displaying a value in millimetres. Adjust this to match the value you previously measured.

And with that, your HTC Vive's lens spacing should be adjusted to your eyesight! Make sure to keep your IPD noted, to quickly adjust the lens spacing at a later date!