Bolivia Zone Question

[jrl]

For Bolivia, the zone is written as follows in southamerica file:

# Zone	NAME		GMTOFF	RULES	FORMAT[UNTIL]
Zone	America/La_Paz	-4:32:36 	-	LMT	1890
				-4:32:36 	-	CMT	1931 Oct
15 # Calamarca MT
				-4:32:36 	1:00	BOST	1932 Mar
21 # Bolivia ST
				-4:00	-		BOT
# Bolivia Time


For this case (third line), I am not entirely sure what the significance
of Rule "1:00" is.  Can anyone shed some light?

Regards,
Jamie