CYA gives that feeling the most. The nice thing is that you can test it then pour the mixture back into the mixing tube and repeat it as many times as you like. I even store mine overnight and repeat it the next day with the same mixture. My results usually start to align and raise my confidence.
In general, hold the graduated vial with only two fingers at the top, at waist level, with sun at your back but with strong sunlight. Basically, you are trying to maximize the amount of sunning hitting the mixture without the direct sun blinding it out. As the sun hits the CYA reagent in the water, it clouds the dot. I find it easier to pour a little in, look around then glance back at the dot. Then add a little more, look around and glance back repeating until its gone. This helps rest my eyes between and keeps the dot from reappearing.