The class char. and the master inspection char. are not compatible

What causes this issue?

You want to assign a class characteristic to the master inspection
characteristic after the master inspection characteristic was created.
The two characteristics, however, are not compatible.
The prerequisites that must be fulfilled in order to assign a class
characteristic depends on whether the class characteristic is of the
data type "<ZH>NUM</>" or "<ZH>CHAR</>."
If the general characteristic is of the data type "<ZH>NUM</>," the
following conditions must be fulfilled:
The master inspection characteristic must be <ZH>quantitative</>.
The two characteristics must have identical units of measurement, if a
unit is assigned to the class characteristic.
The control indicator for the upper specification limit and the control
indicator for the lower specification limit must be set in the master
inspection characteristic.
The interval limits for the class characteristic must be maintained as
follows:

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

<ZH>Master insp. characteristic</> <ZH>Class characteristic
</>
--------------------------------------------------------------------
Lower spec. limit only lower limit, no upper limit
Upper spec. limit only upper limit, no lower limit
Both specification limits both upper and lower limit
If the class characteristic is of the type "<ZH>CHAR</>," the following
conditions must be fulfilled:
A selected set from catalog type 1 was assigned to the class
characteristic.
The master inspection characteristic is <ZH>qualitative</>.
The "Characteristic attribute" indicator is set for the master
inspection characteristic.

System Response

How to fix this error?

Enter a class characteristic that is compatible with the master
inspection characteristic.

Error message extract from SAP system. Copyright SAP SE.