I used to depend on the shop until one day their sensor went dead and they didn't replace it for a month. They just stated the percentages based on the percentages they blended. I promptly bought one and analyzed myself. For the most part they were correct, but I wouldn't take a chance. I dive doubles sometimes. One day I analyzed the tanks marked the information and later on the boat analyzed again. This time during a flow check I opened the manifold that was closed and the gas from the two tanks mixed (something I should have done at the shop before I left but didn't). YIKES! I analyzed again and it was a completely different mix. I had to change the dive plan accordingly.
So in short it is not necessary to have your own analyzer but it is highly recommended to have one. If you don't have one then at least insist on analyzing your fills before leaving the shop and absolutely never dive any mix that hasn't been verified. You never know if they made a mistake or you accidentally grabbed the wrong tank or whatever. If the mix is far from what you expect it to be, then double verify it with another analyzer in case the sensor on one is expired. If two sensors agree, then respect the new MOD or have them correct the fill before you leave.
Dive boats around here expect you to sign off their papers that you analyzes and what it read. But you can leave the dive shops without ever analyzing anything.
So in short it is not necessary to have your own analyzer but it is highly recommended to have one. If you don't have one then at least insist on analyzing your fills before leaving the shop and absolutely never dive any mix that hasn't been verified. You never know if they made a mistake or you accidentally grabbed the wrong tank or whatever. If the mix is far from what you expect it to be, then double verify it with another analyzer in case the sensor on one is expired. If two sensors agree, then respect the new MOD or have them correct the fill before you leave.
Dive boats around here expect you to sign off their papers that you analyzes and what it read. But you can leave the dive shops without ever analyzing anything.
