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Temperature Unit Conumdrum

Forum|Forum|10 years ago
November 23, 2015
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I'm using Mathcad 15 on a Windows 7 machine. Despite having read this article

Temperature Units

I'm still very confused. In the attached file, the first line I would have expected the results to be 80C. However you can see I don't get that answer. I thought I was not understanding temperature units and that still may be the case. I have found, that to get the correct answer, that the equation has to be written and then edited to get the correct answer. So you can see that the two equations give two completely different answers. I was able to get the correct answer by typing 0C and evaluate the answer and then editing to -20C. Do I still not understand units (a question than really can't be answered) or is there some error going on here?

1_TempOddness-xmcd.zip

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Best answer by MJG

Although it's impossible to tell by looking, your first equation is actually:

-(20°C)+100Δ°C

and your second equation is:

(-20)°C+100Δ°C

note the position of the parentheses.

In the first equation, Mathcad is calculating 20°C and storing the value in the background as 293.15°K, then it applies the negative sign.

Negatives and temperature units are finicky in Mathcad. Maybe other users have suggestions on how to cope.

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Although it's impossible to tell by looking, your first equation is actually:

-(20°C)+100Δ°C

and your second equation is:

(-20)°C+100Δ°C

note the position of the parentheses.

In the first equation, Mathcad is calculating 20°C and storing the value in the background as 293.15°K, then it applies the negative sign.

Negatives and temperature units are finicky in Mathcad. Maybe other users have suggestions on how to cope.

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Thank God there are no tall bridges between work and home today or I might be tempted to jump.

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