Window trimming quality score calculation

[s-j-mc]

Hi,

When window trimming the reads, how is the average across a window calculated? Is this simply an average of the quality scores, or are quality scores first converted into an error rate, an average error rate calculated, and this converted back into a quality score?

Hopefully this link describes what I am referring to (https://community.nanoporetech.com/posts/what-is-the-base-value-for), particularly Patrick Bohn's and Stephane Plaisance's comments.

Stephane also points towards another link:
"I found reference to this topic by reading about arithmetic vs geometric use for averaging (https://gigabaseorgigabyte.wordpress.com/2017/06/26/averaging-basecall-quality-scores-the-right-way/)"

As I am intending to use multiple tools for reviewing data, I'd like to know this so I can account for differences I may see in outputs.