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Evaluation type: eval units
Evaluation type: eval units

Everything you need to know about the evaluation type: eval units

Updated over a week ago

This evaluation type checks the (numerical) answer of the student as well as the unit they used. Before comparing the student’s answer to the Solution, both are automatically converted to base units, e.g. if the student’s answer is 100m and the Solution is 0.1km, then the answer will be regarded as correct.

In the Definition field, you should write the solution using a backtick ( ` ) between the value and the unit.

Example:

A list of all available units and their notation can be found in the authoring manual. Note that combinations of units in this list can also be used, e.g. m/s can be used since m and s are in the list. The conversion to base units is done by the Maxima package ezunits.

Note that this evaluation type does not have automated feedback. The system does give a warning if the unit in the student’s answer is not recognizable:

The correct way to indicate the unit Pascal would be `Pa`.

### How the student should input a unit

The student should input an answer using the unit button on the unit tab of the virtual keyboard.

The student should write the value in the first field and the unit in the second field.

If students don’t use this button, the letters in the student’s answer will be seen as variables instead of units.

To help the student remember that they should use a unit, or to make it easier for them to input the unit, you could add a `#\unit{\box}{\box}#` placeholder in the texts tab.

When you do this, the unit structure will already appear on the screen when the student loads the exercise.

The units themselves can be inputted using the unit tab on the virtual keyboard or by using letters on a physical keyboard. Units are case-sensitive.

For checking numerical answers, there are two options:

• Range: the system checks whether the answer is within the closed interval `[ range low , range high]`. Note that we need to write the lower and upper range in the same notation as in the Definition field, so including a backtick and the unit.

• Precision: this field defines the accepted absolute value of the margin of error for the numerical answer. Just a number suffices in this field. The unit of the Definition field will be used.
Example: If the correct answer is `1`m`, you can use a precision of `0.1` to accept all answers in the closed interval `[ 0.9`m , 1.1`m ]`.

If both range and precision are specified, the system only looks at the range specification and ignores the precision specification.

If both range and precision are used, but the range specification is not written down correctly (for example by forgetting the unit in the lower range), then the evaluation type does not work at all. Example: the solution rule below will not work (i.e. it will not evaluate any student’s answer to ‘correct’):

More on evaluation types

An overview of all evaluation types can be found here (for mathematical answers) and here (for text-based answers). More detail on the different fields of a feedback rule can be found here.