Correction to: J. Eur. Opt. Soc.-Rapid Publ. 16, 19 (2020)

https://doi.org/10.1186/s41476-020-00140-9

Following publication of the original article [1], we have been informed that on Page 9, the circular chord equation (equ 3) is given. Under the root sign we have the term: 2rh - r^2 but it should be: 2rh-h^2.

The original article has been corrected.