API Test Kit: which way is correct ?

[topgundcp]

When testing for Nitrate, the instruction says that The tube should be viewed
against the white area beside the color chart. If I put the tube on the white area touching the card, The color is close to read 20ppm, but if I leave a little space between the tube and the card, it would read 10ppm. Which way is correct ? please advise. Thanks

 

[loyalrogue]

Good question.

I found that when I held it against the card it seemed that the glass tube was creating a shadow that made the results look darker.
Now I just hold it up in front of a well-lit wall.

FWIW, I've never bothered to ask what the proper way is so I could be doing it wrong.

 

[Devilishturtles]

Hmm. I hold it directly against the card, but in front of a light too.