All websites should have some sort of statistics package installed on it to allow you to track the progress of the website. Many hosting companies offer a basic stats package that is installed on the server that will usually show you the visits to the site, pages viewed and possibly the source of the traffic (i.e. if the visitor has come from Google, Bing or direct etc.).
Google offers a stats package called Google analytics. The software is free to use at present but you may incur a small charge from your programmer to install the code on to your website. This allows you to drill down a lot deeper in to each visitor, finding out not only where they have come from but what keyword or phrase they typed in to find you, the pages they visited, time spent on the site and even the page they exit the site on. It also allow you to set up goals to track a visitor – so for example you could set up a goal that tracks every time someone fills in an enquiry form or uses a calculator on your site. You can then track this visitor to see if they make a purchase or contact you.