Cessna 172R Pilot Operating Handbook page 296

The DME arc IAF identifier may be unfamiliar. Example: D098G
where 098 stands for the 098° radial off the referenced VOR,
and G is the seventh letter in the alphabet indicating a 7 DME
arc.
APRARM to APR ACTV is automatic provided:
Your in APRARM (normally automatic).
You are in LEG mode.
The FAF is the active waypoint.
Within 2 nm of the FAF.
Outside of the FAF.
Inbound to the FAF.
RAIM is available.
Direct-To operation between the FAF and MAP cancels APR
ACTV. Fly the missed approach in APRARM.
Flagged navigation inside the FAF may usually be restored (not
guaranteed) by pressing the GPS APR button changing from
ACTV to ARM. Fly the missed approach.
The instrument approach using the KLN 89B may be essentially
automatic staring 30 nm out (with a manual baro setting update)
or it may require judicious selection of the OBS and LEG modes.
APRARM may be canceled at any time by pressing the GPS APR
button. (A subsequent press will reselect it.)
SECTION 5
PERFORMANCE
There is no change to the airplane performance when this avionics
equipment is
installed.
However, installation of an externally-
mounted antenna or related external antennas, will result in a minor
reduction in cruise performance.
S5-16
Dec 2/96
SECTION 9 - SUPPLEMENTS
CESSNA
SUPPLEMENT 5- FAA APPROVED
MODEL 172R