# [std-proposals] On the standardization of mp-units P3045R1

From: Tiago Freire <tmiguelf_at_[hidden]>
Date: Tue, 18 Jun 2024 12:28:11 +0000
Hi, I will be participating in St. Louis.
And one of the papers that interested me was P3045R1, unfortunately I may or may not be on time to participate in this particular session.

There’s this question that I would like an answer too, and I wonder if there is anyone who will be attending St. Louis who would be willing to make this question on my behalf:

A lab worker puts in 40Kg of dry ice into a 1 cubic meter pressure tank rated for 10atm, they then vacuum the tank and seal it.
As the CO2 warms up to room temperature (which at a specific date was 28°C) it evaporates, and eventually following the ideal gas law:
PV=nRT

Is this setup dangerous?

Using mp-units (with the exact same design as the one being proposed for standardization) to solve this problem:

```
quantity Volume = 1.0 * m*m*m;
quantity Temperature = (28.0 * deg_C).in(K);
quantity n_ = 0.04401 * kg / mol;
quantity R_boltzman = 8.314 * N * m / (K * mol);
quantity mass = 40.0 * kg;
quantity Pressure = R_boltzman * Temperature * mass / n_ / Volume;
std::cout << Pressure << std::endl;
```

We get the following result:
`211581 N/m2`
(=211.581kPa = 2,09 atm)
But the correct answer is actually: 2275.629kPa = 22.5 atm
(11 time s higher than what mp-units calculated)

How is this considered a design feature and not a bug? (note that other similar libraries don’t have this problem)
And how do the authors think this design choice impacts on safety and user-friendliness?

Thanks.