One thing I have found helpful on Nitrite especially is to do a mix of tank and tapwater (I have a true graduated pippette which helps with this) and try to get the mix to have a lower Nitrite (0.25 or 0.5 ppm which I find easier to read) then just multiply to get the true tank water result.
This also works when your readings are off the scale...
This also works when your readings are off the scale...