CYA Testing in the Sun

[Deb04]

When I do the CYA test, back to the sun, sun over my shoulder, should the sun be shining through the side of the tube or should it be in the shade? I get 5-10 ppm lower if I hold it in the shade.

 

[pooldv]

In the shade, back to the sun. Here are some reference pics, https://www.taylortechnologies.com/ChemistryTopicsCM.ASP?ContentID=36

 

[JoyfulNoise]

It should be held waist high in the shadow cast by your body. You fingers should pinch the top of the tube to hold it but do so with the least amount of the tube occluded by your fingers. Basically you want bright, indirect light shining into the tube. This produces the best result with minimal reflections.

 

[MarianParoo]

Nice explanation, JFN. I would emphasize the shadow cast by your "body". My neighbor didn't hold it correctly and kept seeing the shadow of her "head" and thought it was the dot.