How is Precision used to calculate critical chance?

I am very confused by the Precision attribute. On the Guild Wars 2 wiki it says:

Precision is an offensive character attribute. Attribute points put into precision increase the chance of a critical hit for the character. Many of the conditional effects of a skill or trait trigger on a critical hit.

What confuses me is, how critical strike is calculated from precision. I had previously had 47% chance to critically strike (when I was about lvl 40). I am now lvl 60 and when I looked it says I only have 40% critical chance. I know for a fact that I have way more points of precision now than when I had 47% critical chance.

The only reason for this that I can think of is that the equation to calculate critical chance from precision takes level in account. But I would appreciate if someone give a definitive answer on how critical strike is calculated.

All characters start with 4% natural critical chance.

Your base precision is effectively ignored by the system. Additional critical chance is only provided by precision from your weapons/armor/jewelry/traits.

The amount of additional precision (not base) required to increase the chance of a critical hit by 1% is determined by the following formula, where Level is your character level:

0.0025 * (Level^2) + (0.05 * Level) + 1

Source: http://wiki.guildwars2.com/wiki/Precision

So, at level 80, you gain 1% critical chance every 21 additional precision.