Manual flash photography with old flash and rangefinder camera

[Compaq]

Soo, I've got a black Olympus 35 SP in great shape. I also found a decent vivitar 2500 flash at a thrift store for around 20 dollahs. Here's how I'm currently doing it:

- find exposure for background.. set the exposure, for example (ASA 400): f/5.6, 1/125th
- check my flash-to-subject distance, and read off the flash which aperture will properly expose the subject, for example f/11
- change aperture value, and change shutter speed accordingly as not to affect the end exposure: f/11, 1/30th
- underexpose the background by 1 or 2 stops by adjusting the shutter speed to 1/125th
- Press the shutter


Is this the correct way? It's not very time efficient, at least not in the beginning Maybe I'm messing up my exposure this way I won't know until I (get the film developed).

 

[Compaq]

This is where I've been reading:

http://www.ph.utexas.edu/~yue/misc/35SP.html

(ctrl+f: fill-flash on sunny days)