A control device performs: acquiring an optical measured scan value; setting a measured offset using the measured scan value by reference to predetermined correlations; and determining a control value using the measured offset amount. The control value is used for controlling an amount of colorant to be ejected during printing. In the predetermined correlations, a first pair of scan values is associated with a first pair of offsets. A second pair of scan values is associated with a second pair of offsets. The first and second pair has a first and second scan difference between the scan values, respectively. The first and second pair of offsets has a first and second offset difference between the offsets, respectively. The first scan difference is different from the second scan difference. The first offset difference is same as the second offset difference.