A real-time countdown

A given number (X) should be decremented by (Y) with each unique visitor to the site. For example, if X = 10.99 and Y = 0.01 it would take 1099 visitors to the site to decrement X to zero. A further requirement is that the countdown is available to third party websites. Unique visitors to third party pages (where the countdown is displayed) should also decrement X by Y. As there is only one value of X at any given time this value should be stored server-side. As changes to X are made the value of X should be updated on all pages where the countdown is displayed. Two scripts are required: 1. A server-side countdown script 2. A client-side script to display the countdown In all instances where the countdown is displayed X should be updated in real-time. This suggests that fairly heavy communication with the server is required to constantly check the current value of X (up to a 100 sites could at update or read X at any given time). Perhaps the server could periodically broadcast X’s value to all clients? Use of PHP & JavaScript preferred.