## #19 Convert the unity of the constants g->kg

open
nobody
None
5
2011-11-29
2011-11-29
Luc Couturier
No

All the calculations are made with grams. Why not.
But all the fundamental constants are different because of that!
We can't make a simple calculation in kg, we have to convert each constant into kg, otherwise all the calculations are false ( I know, I experienced that !).
For example, if I make a calculation with the planck constant, I have to convert all other terms into gram because of the 10^-3 factor....and for some expressions it can be very hard !

It very dangerous because if we don't notice all the calculations are false.
If there is no improvement, I can't use this software anymore.

## Discussion

• I don't understand your complaint/request. Can you provide an example?

• Luc Couturier
2011-11-29

Sorry. I think I was not clear (even for myself maybe).

It's just that every constant which is not saved in qalculate must be converted in qalculate units system.

Just imagine an expression X=m^(3/2) given in kg^(3/2) which has a certain value (which you have)
To use qalculate, you have to make the conversion : X[g]=X*31622.77g^(3/2)
If I didn't make a mistake. Not so simple if you need to enter 5 or more other terms.

And each time you will use qalculate you won't remember to convert in g.
At least, it would be nice to have the numerical value of the constant in SI dimensionless.
If I want to make a calcul with SI, I can without converting all the data of the problem. I won't have the units but I can make the calculation quickly!
Because the fundamentals contants in qalculate units system are not very practical.

And at least, inform the user that it's not the SI units! Personnally, at the beginning I just thought it was the SI units and I made many wrong calculations because of that....

I hope I was a little more clear.

• I still don't follow. Can you provide specifically a short example expression that you are entering into qalculate? Something like: "planck*(10 kg)/(30m)" .

I think what you are asking is for units to default to SI units. Another feature request is about this (# 2948676). Unfortunately, this has not been implemented, and development for qalculate has stalled.

• Cousteau
2012-09-03

I think I understood the problem. The problem is mostly that you're storing the wrong value. For example, `electron_mass` is neither `9.1093826e-28` nor `9.1093826e-31`. Those aren't even masses, they're just numbers. The mass of an electron is `9.1093826e-31 kg`. You must specify 9.1093826e-31 of "what" in order to have a meaningful mass; otherwise those could be pounds, micrograms, tons...

If you specify that something is in grams, kilograms or pounds, Qalculate! will do the needed conversions. Also, if you use other units in the formula where you use the constant, the units you get in the result will make sense.