Question about Alkalinity

[Pkern]

When I went to the pool store, they recorded my alkalinity as 38* - with a note on the asterisk saying that this is a calculated number based on CYA...
I tested my alkalinity, and it is at 80. Here's my question: Why do they tell me to add 16 lbs. of alkalinity up?
For convenience I have them test my water and I was also curious if my numbers match theirs. (I have a TF-100 with a speed stir, and an electronic Salt and PH tester)
One last question - I am curious why we are instructed to wipe the tip of the 12 bottle with a damp cloth after each drop when testing alkalinity? Thanks in advance!

 

[mknauss]

TA - Further Reading

www.troublefreepool.com

Don't go to pool stores to test your water. Use your test kit -- the best there is.
They use 'adjusted' TA. That gets you to buy their high priced baking soda. Then the next time your pH is 'high', so you have to add acid. Rinse and repeat.
Wiping the tip of the R0009 is for the first couple uses when new. Static electricity can build up on the tip and cause small drops.