CALLMESHAG: Your vintage Mirro is the type pressure cooker with the weighted regulator, commonly referred to now as a "jiggler'. The directions for these older appliances are fairly universal, with the only possible variance being the ppsi [pounds per square inch]. I believe the MIRRO cookers are 15ppsi. The instructions would be straighforward. With this in mind, any manual for a similar cooker will suffice for the basics.
However, I would advise you to be sure your gasket and other parts are in good working order, and that the pan and lid are both sound. MIRRO cookers are cast aluminum. Older ones are prone to stress cracks, especially ones that have been dropped. Make sure the lid and pan line up properly and that the rims of both are true to round. If the gasket is dried out or cracked, it should be replaced, and that might be problematic for this older model. Gaskets are designed to be used only with the model for which they are made, so substituting is not recommended.
Before resurrecting this cooker for practical use, do a test drive, to make sure it comes up to pressure and performs as it should in every respect. Test drives are done using water only, no food. You can find out more about this at www.missvickie.com
A cautionary note: Older pressure cookers such as this one lack the integrated safety features that are now standard on newer models. Especially important are the pressure lock which prevents the cooker from being opened before all pressure has been released, and the over-pressure release that safely vents excess pressure without calamity. You might consider getting a new cooker just for this reason alone. I realize you have financial restraints, but in this case we are looking at safety as well as value. There are economically priced cookers on the market. Even some of the stainless ones are reasonably priced.
Edited by amazingrace - 10/21/10 at 11:40am