Compute electrical conductivity ratio based on salinity, temperature, and pressure (relative to the conductivity of seawater with salinity=35, temperature68=15, and pressure=0).

```
swCSTp(
salinity,
temperature = 15,
pressure = 0,
eos = getOption("oceEOS", default = "gsw")
)
```

- salinity
practical salinity, or a CTD object (in which case its temperature and pressure are used, and the next two arguments are ignored)

- temperature
*in-situ*temperature (\(^\circ\)C), defined on the ITS-90 scale; see the examples, as well as the “Temperature units” section in the documentation for`swRho()`

.- pressure
pressure (dbar)

- eos
equation of state, either

`"unesco"`

or`"gsw"`

.

Conductivity ratio (unitless), i.e. the ratio of conductivity to the conductivity at salinity=35, temperature=15 (IPTS-68 scale) and pressure=0, which has numerical value 42.9140 mS/cm = 4.29140 S/m (see Culkin and Smith, 1980, in the regression result cited at the bottom of the left-hand column on page 23).

If `eos="unesco"`

, the calculation is done by a bisection root search
on the UNESCO formula relating salinity to conductivity, temperature, and
pressure (see `swSCTp()`

). If it is `"gsw"`

then the
Gibbs-SeaWater formulation is used, via `gsw_C_from_SP()`

.

Fofonoff, P. and R. C. Millard Jr, 1983. Algorithms for computation of fundamental properties of seawater.

*Unesco Technical Papers in Marine Science*,*44*, 53 pp.Culkin, F., and Norman D. Smith, 1980. Determination of the concentration of potassium chloride solution having the same electrical conductivity, at 15 C and infinite frequency, as standard seawater of salinity 35.0000 ppt (Chlorinity 19.37394 ppt).

*IEEE Journal of Oceanic Engineering*,*5*, pp 22-23.

For thermal (as opposed to electrical) conductivity, see
`swThermalConductivity()`

. For computation of salinity from
electrical conductivity, see `swSCTp()`

.

Other functions that calculate seawater properties:
`T68fromT90()`

,
`T90fromT48()`

,
`T90fromT68()`

,
`computableWaterProperties()`

,
`locationForGsw()`

,
`swAbsoluteSalinity()`

,
`swAlpha()`

,
`swAlphaOverBeta()`

,
`swBeta()`

,
`swConservativeTemperature()`

,
`swDepth()`

,
`swDynamicHeight()`

,
`swLapseRate()`

,
`swN2()`

,
`swPressure()`

,
`swRho()`

,
`swRrho()`

,
`swSCTp()`

,
`swSR()`

,
`swSTrho()`

,
`swSigma()`

,
`swSigma0()`

,
`swSigma1()`

,
`swSigma2()`

,
`swSigma3()`

,
`swSigma4()`

,
`swSigmaT()`

,
`swSigmaTheta()`

,
`swSoundAbsorption()`

,
`swSoundSpeed()`

,
`swSpecificHeat()`

,
`swSpice()`

,
`swSpiciness0()`

,
`swSpiciness1()`

,
`swSpiciness2()`

,
`swSstar()`

,
`swTFreeze()`

,
`swTSrho()`

,
`swThermalConductivity()`

,
`swTheta()`

,
`swViscosity()`

,
`swZ()`

```
stopifnot(abs(1.0 - swCSTp(35, T90fromT68(15), 0, eos = "unesco")) < 1e-7)
stopifnot(abs(1.0 - swCSTp(34.25045, T90fromT68(15), 2000, eos = "unesco")) < 1e-7)
stopifnot(abs(1.0 - swCSTp(34.25045, T90fromT68(15), 2000, eos = "gsw")) < 1e-7)
```