I need to measure -0.02 and +0.03wc.

mount it inclined 10:1 for 10 times the resolution. https://www.amazon.com/Yellow-Jacket-78075-Water-
Manometer/dp/B0038QHTK2/ref=sr_1_5?ie=UTF8&qid=1520466840&sr=8-5&keywords=manometer

its graduated at 0.25 intervals and you can easily judge 1/5 of that. So, 0.25 included 10:1 the 0.25 would then be 0.025 and I could fairly accurately judge 1/5 of that or 0.005.

thoughts?