Instruction: Generate an answer to the question by utilizing the information contained in the document.

Input:
Question: Why does the reading say ---?
Document: When ordered, I didn't expect this tool to function as effectively as it does. it checks te hardness of water and delivers a digital reading
And I bought a bottle of distilled water and the reading was the same as in air - exactly what it should have been. There is no way for me to determine the absolute accuracy of the readings, but it serves my purpose quite well. It is small enough to take with me when I travel to test the local water quality.
The second round of testing results were vastly different. As much as 30%-50% different from the readings a few hours earlier. I did a third test awhile later with varying results again.Since I can't judge which, if any, of the reading are the most accurate, I'm returning the meter.
You'll get an instant reading. Just remove, dry off (or flick-dry) and press the on/off button again.The only real downside to this tester is that it really just does one thing: tests dissolved solids. So, if all you care about is how well your water filter is working? You're set here. Otherwise, if you need pH or water temp, you'll have to look elsewhere.
And yes, there are areas that bad in this country. But not many.This Meter is meant to understand whats going on behind the scenes of your water. It does not mean a low reading is safe. It just means there are less dissolved solids which is necessary tool in reef keeping, food/drink creation, among other things. It WILL NOT meter safety concerning E.Coli and other bacteria.
We have had the Zero water filter for more than 6 months. It works great as far as I can tell. We live in North Carolina and have a deep water well. The reading on our well water is .060 all the time it has not varied once. The water after zero starts out at 000. We have changed the filter one time about a month back. We got more than 5 months from one filter and we fill about 12 times a week.
Very interesting to see the readings this device gives. I'm rating it 3 star because I keep getting different result when sampling the same water over the course of a couple of hours. In general however the reading on it is useful and give a good idea on the particulates in a given sample of water. My well water unfiltered register a high reading every time. After filtering through my water filter it drops significantly.
I purchased this device to check the performance of a water filter I purchased here on Amazon. To my dismay, I learned the water filter was virtually useless. The filtered water was almost the same as the water straight out of the tap. I checked the water from my new Samsung refrigerator and its internal filter was much better than the big under sink filter I purchased. The Samsung refrigerator filter reading was about half of the incoming water reading.
I received the tester yesterday. I tested our well water from the tap, our well water with a Brita faucet filter, bottled Spring water from our local grocer, our refrigerator filtered water, Brita pitcher water, and Reduce filter pitcher water.The lowest reading I received on any of them was 107, that was the Brita Pitcher filter. The highest reading was 230 from the Brita faucet filter (it had recently been changed and properly flushed), the unfiltered well water was 130, hmmm.
We bought a Zerowater pitcher for the fridge, so I bought an extra water tester for when I'm out of town. I travel in Arizona and Nevada, so it's interesting to see the values of different locations (last week's measurements in Las Vegas was about 413 ppm). I've only been using it for a little while, so I can't say how long the batteries last. They're designed to be a quick change, and are easy to access.
Answer: I don,t know. I tried mine out again, and I couldn't get it to give me that kind of indication. Sorry.