I did a lot of reading over the weekend, that has brought up additional questions.

Richard, your explanation of saturation with calcium carbonate only being necessary to protect the plaster makes perfect sense. so:

1) How does one determine when the water is fully saturated?

2) If CYA contributes 1/3 of its ppm to TA, how much does Borate contribute to TA? (Assuming the Methyl Red/Bromcresol Green indicator--so that we know what the pH endpoint is)

3) How is Saturation index determined?