How to wire a new Honeywell RTF6580WF thermostat to replace a Chronotherm IV?
Make a list of all the terminals, and the color of the wire that connects to each.

Rc - Red
R - Jumper
W - White
etc.

Next turn the breaker off for the furnace, and/or switch off the serviceman switch for the furnace.  Then open the service panel on the furnace.  You should be able to locate the control board where these wires connect, which should tell you everything you need to know.