I have seen several 0.01 certs and I generally don't trust them mucyh. 0.0051 is also a 0.01. I think for a lot of my standards the AA people just used 0.01 instead of the word "trace": i.e. it is there but too low to measure with their instrument. If you have a good instrument, you may find the 0.01's all over the place, some being closer to 0.001. Also be careful of your curve fitting equation. With the above data set, a 4th or 5th order equation will give a great fit, but be nonsense. Keep the degrees of freedom as high as possible and only use a higher order equation when many of the points show that useful. Remember too that the reason for curvature will often be due to things in nature that are logrithmic, and most curve fitting algorithims try to get by with power series fits. Such problems as readsorption, capacitance limits, and amplification are similar to natural logs not to power series.

David