Calcium Test Kit Readings

I just wanted to see what others' experiences were reguarding their Calcium
Test Kits.

I recently bought one that was on sale at an LFS and I am unhappy with it.
The reason being is that the color change of the fluid is so gradual that it
is very difficult to tell when to stop adding the solution.

With this kit, you take a sample of water, then add 3 drops from bottle #1,
(which makes the sample look real cloudy) mix, then add 7 drops from bottle
number two (turns it real pink, almost red). According to the chart it
should be a light pink at this point but it is way off. Then you start
adding drops from bottle #3. You multiply the number of drops by 20 and
that gives you your mg/L. (which I think is the same as ppm right?)

My problem is, is that the sample never matches the color on the chart
exactly. Supposedly, it will change from light pink to violet (they give
you two colored boxes to compare it to) when the test is complete. It goes
through so many shades of purple and red and it never matches the colors on
the chart. It is impossible to get a good reading.

According to my results I appear to be somewhere between 460 and 540 ppm.
(this is where I matched the end color the closest between 23 and 27 drops)

That seems a bit high and that accuracy range is not acceptable.

I've read that the salifert kit will get you within 10mg/L.

How exactly does the salifert kit work (I mean instructions wise) is it easy
to tell where your reading is or are you doing the guessing game with the
color matching?

TIA SSL

~Mort