Hi, I don’t know if this is considered a Brian question or not.

I am trying to write a calcium concentration equation:

The gating variable of m_s is dependent on the calcium concentration.

where \gamma=30000 /cm, F is faraday constant, [Ca_0]=0.01umol, K_{Ca}=0.4/ms,

Hill coefficient, H=4.6, C_{50}=0.35umol.

## What I wrote:

```
from brian2.units.constants import faraday_constant as faraday_const
iCah = gcahbar*m_Cah*(v-eCa) :amp # gcanbar[mS], v[mV], iCah[uA]
dc_Ca/dt = -iCah*30000/cm/(2*faraday_const)- 0.4/ms*(c_Ca - 0.01*umol) : mol # !??
Gcan = (c_Ca/mol)**4.6 :1
Gcan50= 0.01**4.6:1
minf_Sk = Gcan/(Gcan + Gcan50) :1
dm_Sk/dt = (minf_Sk - m_Sk) / (4.0*ms) :1
iSk = gskbar*m_Sk*(v-eK) :amp
```

the units in `dc_Ca/dt`

is: `uA*1/cm/(columb*mol) - 1/ms (mol - umol)`

The problem is the dimension of equations 1 and 2.

```
nconsistent units in differential equation defining variable c_Ca:
Expression "(((- iCah) * 30000) / cm) / (2 * faraday_const) - (0.4 / ms) * (c_Ca - (0.01 * umol))" uses inconsistent units ("(((- iCah) * 30000) / cm) / (2 * faraday_const)" has unit m^-1 s^-1 mol; "(0.4 / ms) * (c_Ca - (0.01 * umol))" has unit kat)
```

Thanks for any guide.