books lines equal to magnetic declination
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# lines equal to magnetic force
# lines equal skew
# line equal to magnetic inclination
# magnetic declination
# magnetic declination angle
# lines equal to snow
# lines equal speed
# isomagnetic line
# atmospheric pressure lines
# isothermal lines
# Equivalent temperature lines
# isobaric lines
# line equal height
# Equal cost line
# Line equal to the transportation cost
# line equal thickness
# line equal size
# line of equal luminosity of the sun
# line of equal depth
# line is equal to force
