These pH strips have 2 coloured squares on each strip which will change colour according to your pH or your urine or saliva. I have only used these for urine as I read in The PH Miracle: Balance Your Diet, Reclaim Your Health
that urine (first thing in the morning) is more accurate than saliva testing. (The instructions state you test your saliva OUTSIDE your mouth for anyone still wanting to test saliva but worried about putting chemicals, etc in their mouths). The results are ready in 15 seconds and you then compare the colour of your strip to the chart on the packet. The colours aren't always completely easy to match up, and for this reason it helps that there are 2 different colours on the strips and I generally just take an average if it's a little unsure (ie. if one colour indictates around 6.5 and the other 7, I'll decide my reading is 6.75).
The results seem to be reproducible, as far as using several strips for one sample appeared to give the same results in each strip. While following an alkaline diet, my results were rather erratic initally and I wondered were the strips measuring anything at all, but I enlisted my husband's help to measure his pH as he was following the exact same diet as myself. His results tallied with mine remarkably - yes, his was as erractic as mine, but in the very same pattern with similar peaks and lows and the same times. The only thing I do wonder about is how accurate their scale is, as I didn't get to compare them with any liquid of a "known" pH.
So, in summary while the pH strips seem fairly good at giving an indication of where your pH lies on the scale, I wouldn't rely on them to tell me the exact figure due to the difficultly in matching colours, but it is definitely easy to have a good idea where your pH may lie.