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rstraley1-Visitor
1-Visitor
October 13, 2015
Question

Plot Values of psi are off by a factor of 386 in MathCad 15

Once I add units to the variable, the plot value is off by 386. If I change the units to lb/in^2 the result is correct. However, the units for pressure are NOT lb mass. I tweaked settings in Tools/Worksheet Options but I have not found the correct combination.

What did I miss?

3 replies

StuartBruff23-Emerald V
23-Emerald V
October 13, 2015

Randy Straley wrote:

Once I add units to the variable, the plot value is off by 386. If I change the units to lb/in^2 the result is correct. However, the units for pressure are NOT lb mass. I tweaked settings in Tools/Worksheet Options but I have not found the correct combination.

What did I miss?

You missed that Mathcad stores values in terms of base units (eg, Length and Mass) not derived units (eg Pressure).   In addition, Mathcad defines Pressure as pound-force per square inch, so there will be the usual conversion to lb.in/s^2.   You get back the correct display value by dividing your function by psi.

Stuart

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rstraley1-VisitorAuthor
1-Visitor
October 13, 2015

Great response. I am not a power user of Mathcad so I would have never figured this out. Thanks for the timely and informative response.

Randy

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StuartBruff23-Emerald V
23-Emerald V
October 13, 2015

Randy Straley wrote:

Great response. I am not a power user of Mathcad so I would have never figured this out. Thanks for the timely and informative response.

Randy

No problem, Randy.

Stuart

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