Given the deficiencies listed below I was tempted to rate 3 stars but here we have a complete test lab in a kit for only $20 so what do you expect? If half the deficiencies were fixed (mostly related to documentation) it would be an easy 5 stars.Kit has almost everything needed to have your own soil test mini-lab. It comes complete with 2 test tubes, filter device, replacement filters, replacement O-rings (basically rubber gaskets for the filter device since soil is gritty and the O-rings will wear quickly), and a small measuring spoon. This kit and I think most if not all kits work on the principle that:- prepare soil sample (select soil from relevant area of root zone, dry it, pick out the crud, pulverize the sample, don't contaminate it in the process)- use special solution to dissolve relevant nutrient into a solution- filter soil particles out of the solution- develop the solution with a reagent to that either changes color based on amount of target nutrient in the solution or in the case of the K test to precipitate the K (Potassium) out of solution- compare solution against a reference chart.- amend soil based on reference chart results.Starting with previously prepared soil sample it takes me about 35-40 minutes to do all 4 tests (pH, N, P, K) working steadily but not hurrying.I have no way to calibrate my results other than to say that with the exception of the K test the results were consistent with what one would expect of soils in this area. The K test either failed completely each time or my soil is surprisingly deficient in Potassium. The P (Phosphorous) test requires one to do the color compare immediately. The sample starts out with one color and very soon changes to a different color. I think the first color is the correct compare but better directions would be a plus.Kit Deficiencies:- PH scale only goes to 7.5. Much of the West has soils were PH of 7.5 would be considered low. Scale needs to go to 9 or so.- The advertised "40 tests" is probably technically true but misleading. It would be more accurate to say it has enough supplies to do complete pH/N/P/K test on 10 samples. Some tests use more solution than others so perhaps it might not be possible to fully test 10 samples.- Kit assumes you paid attention in chemistry class and learned basic lab process, how to measure and are aware of contamination potential from hands, tap water, etc. Perhaps the tests are not sensitive enough for it to matter hence lack of documentation.- filter device is a narrow tube and the soil solution extract is relatively viscous so solution will not pour out. You could argue it is common sense how to get it out but some basic lab hints would have been a nice addition.- There is a full page of fine print in the directions about how much of which nutrient to add to soil to correct deficiencies. I found about half of it baffling. A consumer-grade test kit should have at least links to a web page with better directions on what to do next.- An FAQ page outlining basics of what to look for when tests seem to fail would be helpful.- There are some givens in soil science such as significantly raising pH is not practical over large areas and is a process that takes years. Again- a few carefully chosen web links would have been nice.- No mention of where to buy replacement solutions, filters, etc.- One of the tests calls for half a measure of a reagent but measuring spoon is for full measure and of a shape that makes it impossible to accurately measure out half a spoon. Spoon is tiny- think 1/20th or less of a teaspoon.Assuming I figure out my soil really is deficient in K instead of the kit being faulty I would buy this kit again. Photos attached- sorry they are not cropped.