Making large constants in C source more readable?

Question

I\'m working on some code for a microprocessor.
It has a few large, critical constants.

#define F_CPU 16000000UL

In this case, this is the C

Answer 1

One possibility is to write it like that:

#define F_CPU (16 * 1000 * 1000)

alternatively

#define MHz (1000*1000)
#define F_CPU (16 * MHz)

Edit: The MHz(x) others suggested might be nicer