Sudheer Satyanarayana has provided a handy cheat sheet for those using the Zend_Date component of the Zend Framework listing the default values of the constants it provides.

Date and time handling in general is a problem in programming. For PHP programmers, there's a good library out there that performs all the difficult tasks and provides convenient APIs. Zend_Date has several constants defined. It is good to know what each one of them represents.

You can either come back to this post if you need a reference or you can download the PDF and have it right at your fingertips.