# Fixed, point and parent stream conditions - Definitions

The fixed, point, and parent stream condition calculations are different types of calculations that reconcile the total (stream) volume in a different manner. These options appear only when using concentration units. A description of each calculation type is given below.

Note: Sometimes to avoid confusion, users change units to moles)

**Fixed condition**

Fixed condition assumes that the total volume at the indicated/given temperature and pressure is 1 L (default) or the entered stream amount.

For example, if the fixed condition is 25 °C and 1 atm, the software reconciles the volume to 1 L at these conditions. In other words, this will be the reference volume value. Then the volume adjust to whatever it is at subsequent T and P points.

In a second case, for example, if the fixed condition is 41 °C and 376.8 atm, then the software reconciles the volume at these conditions to 1L.

The fixed condition calculation (we believe) is what the software should do, since as you add material to the stream the volume increases.

**Point condition**

The point condition calculation adjusts the volume to the indicated volume in the stream amount cell for each T and P. For example, if the stream amount is 1L, then the software will make sure that the volume stays constant at the each T and P condition.

The point condition calculation can be seen as calculating different single points.

**Parent stream condition**

The parent stream condition uses the reconciled volume at the parent stream conditions.

In the figures below, you can see that the volume used is the one defined at the original (parent) stream. You can see this as a variation of the fixed point condition, with the difference that T and P can't be modified at the sub-stream level

We recommend to use the “fixed condition” or the “parent stream condition” for the majority of the calculations.