I don't get why you would need to do that ? Given the turn indicator has the rate 1 turn labeled on there. IS that for aircraft that don't have turn indicators ?
Also how long is to turn 180 degrees in a rate 1 bank turn ? I remember being told this on my PPL and have forgotton. I always thought if I, inadvertently, went into cloud I'd look at the DI and wait for it to turn 180 degrees. Although in the heat of battle I'm not sure if I would remember to do that. Isn't it 2mins for a 180 degree turn ?
A standard turn (or rate one) is 360 degrees in two minutes, or 180 degrees in one minute.
Knowing the required bank angle is useful because the AI gives you immediate feedback on the bank angle, while the CDI takes a few seconds to stabilize (because your turn will take a few seconds to roll into and stabilize).