Hobbyists and explorers need a reliable tool to collect important field data and to monitor their tank conditions. In order to do this properly, there has to be some kind of standard to measure against. The most important one being a good test kit.
We know everyone doesn’t have access to costly high-end Lamotte and Hach test kits, which we know are reliable and often used for scientific research. Luckily there are some options that are more affordable but still reliable.
Nutrafin Master Kits are still somewhat costly but are complete and accurate. The shelf life is quite long. It is not unheard of for Nutrafin to have maintained accuracy a few years past their usually assumed expiry date. It is also easy to buy replacement bottles for anything you run through.
Lamotte and Hach are definitely accurate enough for field study. Nutrafin and Sera will be as well for hobbyists in the field as well as those wishing to keep track of their tank parameters.
You will not get multiple decimal point accuracy with the Nutrafin and Sera kits. That level of resolution isn’t necessary unless you are doing very specific and detailed scientific research. They would be close enough for hobby level requirements and for gathering data to aid in the husbandry of aquariums and terrariums. If someone is doing a specific botanical study they may need a high-end scientific test kit.
Hobbyists wanting to have a general but still detailed idea of the parameters needed to keep a certain plant collected for banking purposes, then a good hobby level will do.
To calibrate the kits it is a matter of noting the deviation and adjusting from there. For example, control your source first. Test a ph solution on water you know is neutral. If your test says 0.5 off then you know all your other tests will also be off by that value, etc. and you would adjust your readings by changing them 0.5 up or down.
As far as testing goes. Take multiple samples from multiple locations over multiple weeks, months, and seasons preferably. Make note of not just relevant data sets but also geology, soil, and rock composition, other flora and possible fauna. Write down your findings