We use “few” when we’re counting (and “less” when we’re measuring), But in a sentence like this, the correct term is “two.” “Few” implies three or more.
Older analog hygrometers come in various forms including hair tension hygrometers and sling psychrometers to name but a few.
I suppose the writer could harrumpf and point out that both are plurals, implying at least four, but I don’t think so. The topic is really about two things.
The sentence is from an Interesting Engineering article about weather instruments.
To give the writer credit, he (or she—the article is unsigned) uses correct terms later:
The former, as the name suggests, use animal hair (which is hygroscopic – water absorbing) to ‘detect’ changes in relative air humidity as the hairs length changes.
They tend to be equipped with instruments to measure local temperature, wind speeds, and barometric pressure to name but a few.