Garmin GPS 155XL Pilot's Manual & Reference page 78

ROUTE NAV
SECTION
4
Route RAIM
Prediction
Figure 3
Figure 4
68
The time required for RAIM prediction computation depends on the route
distance (i.e., 1000 nautical miles = approximately 2 minutes) and the enroute speed.
The longer the route distance and the slower the enroute speed, the longer the time.
If RAIM unavailability is detected based on the associated requirement, the prediction
process will stop immediately and display 'NO RAIM' as shown in Figure 4.
'NO RAIM' does not mean RAIM is unavailable for the entire route. This
message results when RAIM unavailability is detected for more than 5 minutes at any
point along the intended flight (based on BRNAV requirements).
If a satellite is listed as 'out of service' by NOTAM, you may use the 'rem
sat' (remove satellite) field to prevent a particular satellite from being used in the
Route RAIM prediction (e.g., removing satellite 9 in Figure 4).
To exclude a satellite from the Route RAIM prediction:
1. Highlight the 'rem sat' field.
K
2. Rotate to select the satellite to be excluded.
3. Press E to accept.
4. Press E again to begin Route RAIM Prediction without using the selected satellite.