Wilko 12" Spirit Thermometer

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What's this "triple point" then? (please explain in laymans terms:D)

Sorry, all! The triple point of water is the temperature at which it can be in all three states, gas, liquid and solid. It is usually called "freezing point" and designates the bottom end of the Celsius scale at 0 degrees Celsius (or Centigrade).
 
Sorry, all! The triple point of water is the temperature at which it can be in all three states, gas, liquid and solid. It is usually called "freezing point" and designates the bottom end of the Celsius scale at 0 degrees Celsius (or Centigrade).

So you mean testing at freezing (0C) as well as boiling point (100C)?
 
So you mean testing at freezing (0C) as well as boiling point (100C)?

Yes! The point being that however the original instrument was calibrated, it was so well made that its readings will be approximately linear, so that if you know two points with some certainty, then all those in between can be estimated with some confidence by using a ruler.

The difficulty here is (I think) marking it up so as to be more useful on a Brewday.
 
Yes! The point being that however the original instrument was calibrated, it was so well made that its readings will be approximately linear, so that if you know two points with some certainty, then all those in between can be estimated with some confidence by using a ruler.

The difficulty here is (I think) marking it up so as to be more useful on a Brewday.

That's how I calibrate my thermometers. If it's out by the same top and bottom I can just adjust by the amount it's out. The problem for me is when it's out by two different amounts. Too much for my poor head to cope with. I once found a graph thingy on the web to work out what the difference is but my head nearly blew up trying to understand it
 
That's how I calibrate my thermometers. If it's out by the same top and bottom I can just adjust by the amount it's out. The problem for me is when it's out by two different amounts. Too much for my poor head to cope with. I once found a graph thingy on the web to work out what the difference is but my head nearly blew up trying to understand it

Yep, That is why I would advise knowing what the key marker temps are on your thermometer's scale. I would guess 65, 70, 75 and 80 are the main ones for a "no chill" brew. Since if you know with some certainty where these are, then you only need to do the maths once and then either it's too low or too high...

Also, even if the thing is out by 5 at one end and 1 at the other, the critical region is a small part of the whole scale.
 
Here's a chart that shows the triple point of water ...

https://www.google.co.uk/?client=sa...XJF7KijBzfJn753BNASYRs=&imgrc=2RYO1XCMCwOtTM:

As you can see, at 0 degrees at atmospheric pressure it can be a solid (ice) or a liquid (water) but to take it to a vapour at the same temperature requires a drop in pressure to +/- 0.1 atmospheres.

My problem is that the thermometer I inherited is accurate ... :thumb: :thumb:

... but I can't read it because the filling has fallen out of the numbers and markers engraved on the stem.

I could do a "down and dirty" job on it by filling in the engravings with a "permanent" marker but when used in hot water they all seem to stop being "permanent" ... :doh:

... plus I don't know how toxic they are!
 
That's how I calibrate my thermometers. If it's out by the same top and bottom I can just adjust by the amount it's out. The problem for me is when it's out by two different amounts. Too much for my poor head to cope with. I once found a graph thingy on the web to work out what the difference is but my head nearly blew up trying to understand it

I used to work calibrating instruments including glass and electronic instruments for lab use. I agree that it would be great if the instrument response was linear by knowing that 0°C and 100°C are correct but not always the case hence the difference at top and bottom. It is best to know what the response is at the temperature you are working at.
So for instance if you are always working at 65°C, that is the area where you should know what your correction factor is, if any, by checking against another reliable instrument.

I have a Hanna electronic thermometer with replaceable probe, cost more than £200 when new. Electronic instruments (high end) usually resolve to 0.1°C and never really vary however if your instrument has a detachable probe then both the probe and the instrument can cause errors and should be recalibrated if you change the probe. I know that this instrument is very accurate, over several years it never varied by more than 0.2°C and I can use it to calibrate any other thermometer I have.
 
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