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Creating New Units

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Hello!  

 

I am trying to create a new unit and having a little trouble with quantity based calculation. 

 

I have created a new unit set entitled "ICE Engines" to deal with units specific to internal combustion engines.  The first unit I am working with relates to spark advance.  Some systems report spark as degrees before TDC (Deg_BTDC), and some report spark as degrees AFTER TDC.  So, these are the same measurement, just opposite signs. 

 

I have created a new quantity called TDC Relative with dimensions 0,0,0,0,0,0,0 and category of rotation, since deg_BTDC is just degrees, but in a relative sense.  

 

For the units the factor for Deg_ATDC is 1 and Deg_BTDC is -1.  This enables the unit conversion to work great, so I can easily convert from Deg_BTDC to Deg_ATDC. This is wonderful.

 

The problem I run into is when I add two of these together in a quantity based calculation. If I subtract 1 Deg_BTDC from -1 Deg_ATDC, I get 0, as I expect, BUT the unit is in Radians, I assume because of the category of rotation. This is really ok, except that I cannot convert Radians back to Deg_BTDC. 

 

If I remove the category of rotation, I again get the correct numeric value, but the unit is "1", so that doesn't work either. 

 

 

 

So, how do I do one (or both) of the following:  Create a unit set that allows quantity based calcultions to result in a unit the new set, or convert a default unit (Radians) into a custom created unit?  

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Solution
Accepted by topic author RussellSenior

It always happens... I spend hours reading, and fiddling, trying to get something to work, so I post on a forum, and 5 minutes later I figure it out....

 

Anyway, in the Dimension Category, you can enter a new category instead of just selecting an existing one... 

 

So, it does what I want now, but any input from the Gurus is always appreciated.  ^_^

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