As info here is the “link” to Century Avionics. http://www.centuryflight.com/pricing/frame/manual.htm
You will find the HSI manual under the “blue link” labeled *68S85. Good reading for those of us “approaching final” Hope this is useful!
This is very useful . . . I didn’t know our SR20 HSI in “C” is a more reliable electric gyro for heading information. If both vacuum pumps fail, we would have additional redundancy here for navigation. Of course, the S-Tec works off the turn coordinator (electric)and, I suppose, the heading bug on the HSI would work too despite vacuum pump failures.