I was looking at some pictures of the DC-9 cockpit and i'm confused on what the dial thing (it kind of looks like a tape gauge like one in a 747) to the left of the engine gauges does. Can someone help? thanks

 

 

If I remember correctly it is the EPR gauge. I forget exactly how it works though. Been 20 years since I ran a DC-9. By the way, that means Engine Pressure Ratio.

Here is a link that should help explain it better.

 

http://tonymadgehjg.proboards.com/thread/4951/question-epr-rat-gauge-dc

Correct - EPR & RAT from the Stellan Hilmerby's excellent site about the DC-9 / MD-8X series. 

Hi jakronym!

Basically without entering in heavy explanations, EPR is the ratio between total pressure at the exhaust(or a station close to the exhaust, just after the turbine) and the total pressure at the entrance of the engine. Then it expresses the"thrust" or say another way the efficiency of the engine. Nowadays with turbofans the N1 is the main parameter to set the thrust of the engine. In the "good old days"(okay I'm not so young)we use the EPR on planes like the DC8 I flew(I flew also the re-engine DC8-72CF with CFM56 and the N1 as main parameter for thrust). Today, the JT8, on the MD, still use EPR for thrust settings. Of course EPR or N1 are not enough, you need also EGT, N1 and N2 to check the good health and power of your engines!

 

Cheers