The warning signal consists of a variation in the
tone of the Siren. This is produced by increasing the speed of the
engine to 3000 R. P. M., or over, and decreasing the speed to 2600 R. P.
M., as shown by the tachometer, completing the cycle in regular
intervals of from 8 to 10 seconds.
When the tachometer is not visible, the required
intervals can be regulated by counting at Army march time. With the
engine speed at 3000 R. P. M., the speed will decrease to 2600 R. P. M.
to the count of 4. To increase the speed to 3000 R. P. M., requires a
count of 12.
To give the warning signal:
- Remove siren horn cover.