So funny story. I went to calibrate my pH pen. Ive had the same combo meter for a few years. I was getting an error message when I was trying to calibrate it. Ended up buying a new probe ($90) and some new calibration solution. Waited 2-3 days to get them delivered, mean while the girls are getting thirsty. I plug the new probe into the meter and get the solution ready. Still getting the same error code. I finally download the manual for the meter. Come to find out I was using the wrong solution first. Doh, stoner moment.