2 Different hydrometers coming up with different readings

[bigalwhat]

I have been using a copper tun hydrometer for as long as i have been brewing, and lately i brought a 2nd hand barrel which came with a coopers hydrometer. I have never used the coopers one until today as I thought the reading on the copper tun one was quite high.
it turns out they are quite different
the copper tun one showed 1017 where as the coopers one showed 1005

here are the photos taken at the same time... should they be different?

coopers


copper tun

 

[Spiesy]

Are they both calibrated to the same temperature, i.e. 20-degrees?

Should be written on the hydro.

 

[danestead]

You could check the calibration on them.

It should read 1.000 in RO/DI water however tap water is probably close enough if you dont have access to RO or RO/DI or distilled.

You can also check calibration at a typical OG of say 1.048 with the following method. You will need some have decent accurate kitchen scales. Mix up 176mL (or grams) of RO/DI water (ideally) with 24g of normal table sugar. This will give you 200g of solution and your hydrometer should read 1.048 when tested at its calibrated temperature (usually about 15 or 20 degrees)

 

[Yob]

What do they read in plain tap water?