Short answer: Unless brevity of calibration is important, you should use spiral calibration.
Also known as smooth pursuit calibration, this has been the standard calibration method used in FOVE since v0.17. Prior to that, FOVE used a series-of-fixations calibration, but it was deprecated and removed in favor of this newer calibration method.
Advantages of smooth pursuit calibration:
Disadvantages of this calibration
Sometimes called single-point, this calibration is included as part of FOVE Pro. The user looks at a single point near the middle of the screen for about a second or two, and the calibration is completed.
Advantages of this calibration method:
Disadvantages of this calibration method:
How much is the accuracy impacted? The following heatmaps show the average accuracy in degrees across many different FOVE 0 users. Measurements were taken for each section of the screen, up to +/- 25 degrees from the center.
Smoot Pursuit Calibration
One Point Calibration
In the center region, both calibrations yield very accurate eye tracker results. As the gaze moves towards the edges, the spiral (smooth pursuit) calibration retains more accuracy than the one point calibration. Across the whole range, the spiral calibration averages about 0.2 degrees better accuracy (as of late 2021).
If you are interested in our benchmarking methodology and how these figures were taken, you can learn more from this paper we published at ETRA '21 (the full text is available if you click on the PDF icon).