Union
$$A \cup B =$$
{ forming, interval, nominal, norming, ordinal, performing, ratio, storming }
Symmetric Difference
$$A \ominus B =$$
{ forming, interval, nominal, norming, ordinal, performing, ratio, storming }
Difference
$$A - B =$$
{ interval, nominal, ordinal, ratio }
Difference
$$B - A =$$
{ forming, norming, performing, storming }
Cartesian Product
$$A \times B =$$
{ (interval, forming),
(interval, norming),
(interval, performing),
(interval, storming),
(nominal, forming),
(nominal, norming),
(nominal, performing),
(nominal, storming),
(ordinal, forming),
(ordinal, norming),
(ordinal, performing),
(ordinal, storming),
(ratio, forming),
(ratio, norming),
(ratio, performing),
(ratio, storming) }
Level of measurement