Suddenly PR4

When my blog was a PR3... I was wondering what's wrong with Google since my blog is basically nothing much and of not much importance except to me. Later when my blog's PR dropped to 2, I was like ok~ nothing much. But when it suddenly shoot to PR4, I wonder whether the PR is that accurate. But alls fine, whether my blog is important to Google or not, its a PR10 blog to me. ;D