hanna ulr phoshate

I just ran 3 tests in a row on my Hanna ULR Phosphate and had 3 different results. (Between .09 2nd test and 3rd I decided to put in a new battery just for heck of it btw) .18ppm .09ppm .21ppm Has anyone else ran a couple to few tests in a row w/ different ranges outside the margin of error...