you know you can't add another decimal there. the swing arm measures 1.023. If you wanted to extrapulate I would say your arrow looks more like 1.0236. at any rate your accuracy is only as good as your smallest measured value. so your swing arm has a accuracy of +/- 0.001

as with anything some are better than others, I got a refractometer from a fiah store and it reads 3 decimal places like the ones here, I picked one up some where else, paid a bit more money for it and it reads 4 decimal places.

One note about floating glass type, the reading changes with changes in barometric pressure, and 3 different people will get 3 different readings off them due to the water meniscus and the angle they look at it. Oh and the break easy :sad:. I use them for making wine only, my tank gets the refractometer (well the wine might also as soon as a find a decient one that is cheep.:mrgreen:)

Steve

It's kinda gettin silly.

First and formost, if you test the bucket of replacemnt water and the tank water with the same piece of equipment (float, swing arm, refractomerer, picnometer what ever..) and the slainity is close or the same great!. If you tank/livestock is doing well at .024 great that means every thing is aclimated to that salinity. If its .019 and every thing is thriving so be it. It simply must be consisitent or a slow change to allow everything to adapt.

If you are having a problem, then worst case senairo take a tank water sample to a local store that has a refracometere and have them test it. Then test with your apparatus. Bob's your uncle. make the changes you need to, and re-test your corrections (for aparatus of choice) on a regular basis.

Easy.

That is regarless of what school of thought you subscribe to in regards to salinity level.

I'll just be buying a refractometer to start off with, to alleviate any issues. I mean, for only 40 bucks, why not?

exactly, it always amazes me that people have no problem spending 500 on rock, and thousands on coral but cheep out on test equipment.

having the most accurate method of measuring your salinity isn't getting silly either, as a lot of problem can come from salinity and if you don't know if your device is off or not how can you find the problem? Just ask Aquattro what happens when you trust old swing arms to much :mrgreen:

Steve

imo, take the hydrometers and throw them in the trash. they are horriably calibrated

switching to a refractometer is probably one of the best things you can do for a reef tank