# What does “up to proportionality” mean exactly?

Using the "site:"-specific Google search, I have searched both MO and math.SE for the word, "proportionality," and have noticed the phrase "up to proportionality" in many posts.

What does "up to proportionality" mean exactly? A link to its source would be nice.

• For example, a certain constant is so (i.e. constant) "up to proportionalty" because its value may change if we change the units of measure involved. – Mauro ALLEGRANZA May 14 '17 at 14:43
• "There is, up to proportionality, a unique triangle with all edges the same length." Something like that? – Arthur May 14 '17 at 14:44
• Related question – Arthur May 14 '17 at 14:44

Depends on context. It usually means that the answer of a problem is only well-defined up to a constant. For example when you compute an eigenvector of matrix, the vector $v$ is equivalent with the vector $5\cdot v$, so one might write a sentence like "the eigenvector is $\dots$ up to proportionality".