word choice - Difference between "change is constant" and "change is a constant"

The boss asked me the other day whether it's more correct to say

In our business, change is constant.

or

In our business, change is a constant.

Both of these sound perfectly correct to me, which is what I told him; but there's a slight difference in meaning that I just can't seem to articulate. Help?

Definitions, not that they're much help:

constant (noun): a quantity that does not vary
constant (adjective): unvarying in nature; steadfast in purpose or devotion or affection; uninterrupted in time and indefinitely long continuing

Answer

I think if your implication is that change is a given, that it is one of the only constants you see in the business, then you use the noun (change is a constant).

If your implication is that all we ever see is change, change, change, change, change then use the adjective (change is constant).