Should I get the Phosphurous Checker?

[tytown]

Ok, feeling better about it tonight. I went at it again but with the approach based on people's comments and some other research and was able to get a spread of readings within the units rated accuracy +-0.03 ppm (+-5% of range; range =200 PPb)
I perfectly prepped the reagent packet to ensure that it would all get in the vial before the test is even started
Grabbed water from the same location in the tank being careful not to get finger water in the sample.
I kept the orientation of the vial the same throughout all tests (10ml facing me)
And I used a fresh microfibre cloth and meticulously buffed the outside of the vial.
After all that it tells me I have 0.09 - 0.12 ppm PO4.
I would have liked to know which of the above had the largest influence on the results and I wonder what my readings would have been if the vial was flipped 180. Unfortunately I can't debunk the errors I went through becuase I only have 4 reagent packs left from my box of 25 bought just yesterday.
I'll use the current levels as a reference from here on out.
Thanks everyone.