There is less error involved with a refract. I have yet seen a Deep-Six that is even close
to what it should read. Swing arms units also have a habit of collecting salt deposits on
the swing arms and pin, which can cause very low readings. Thus, they need to be soaked in
vinegar every month to remove such deposits. Floating hydrometers have the issue of temp
compensation, where most in this hobby seem to get lost. Refracts are much more accurate
out of the box. However, they are also in error but we can compensate for that. For the
last couple of months Randy and I have been colleting data so he could redo the old DIY
calibration solutions from months ago. We knew something was wrong with them and we wanted
something reefers could make easily for a DIY calibration solution. The first ones we had
were to low. In short your refract reads 1.5 ppt to low. So if you want a salinity of 35
ppt (3..5 %), on your refract, it needs to read 36.5, which equals 35 ppt NSW. Refracts
from the factory are not calibrated to seawater but NaCl, which does not have the same RI
( Refractive Index) as NSW. You can read all about it here. It just came out the other day
:-)

http://reefkeeping.com/issues/2004-06/rhf/index.htm

--
Boomer

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If You See Me Running You Better Catch-Up
"Pszemol" wrote in message ...
: "Boomer" wrote in message
...
: About 95 % of the expensive refracts, $200-$300, only go to 1 ppt
:
: Thanks, so why people say refracts are so acurate and reliabe?
: People can get acuracy 0.001 sg with cheap Deep Six swing arm.
:
: Are we paying more just to have a convenience of refractometer?