How many values of r z (arcsecond) correspond with a r y (arcsecond) value of −0.247?
create table table_15318324_1 (r_z___arcsecond__ varchar, r_y___arcsecond__ varchar, PRIMARY KEY (r_z___arcsecond__))
select r_z___arcsecond__ from table_15318324_1 where r_y___arcsecond__ = "−0.247"