▁passed ▁through ▁the ▁Cur ie ▁point . ▁ ▁This ▁involves ▁sufficient ▁mass ▁to ▁take ▁samples ▁from , ▁and ▁a ▁suitable ▁material ▁with ▁ade qu ate ▁magnet ite ▁to ▁hold ▁the ▁rem nant ▁magnet ism . ▁ ▁In ▁addition , ▁the ▁feature ▁needs ▁to ▁be ▁in ▁an ▁area ▁for ▁which ▁a ▁sec ular ▁variation ▁curve ▁( SV C ) ▁exists . ▁Once ▁the ▁pale od ire ctions ▁of ▁enough ▁independently ▁dated ▁arch ae ological ▁features ▁are ▁determined , ▁they ▁can ▁be ▁used ▁to ▁compile ▁a ▁sec ular ▁variation ▁record ▁for ▁a ▁particular ▁region , ▁known ▁as ▁an ▁S VC . ▁ ▁The ▁Arch ae om agnet ic ▁Labor atory ▁at ▁the ▁Illinois ▁State ▁Museum ▁has ▁sec ular ▁variation ▁curves ▁for ▁the ▁south west , ▁mid - cont inent ▁and ▁sout heast ▁United ▁States . ▁ ▁Add itional ▁data ▁points ▁from ▁arch ae om agnet ic ▁samples ▁with ▁corresponding ▁d ating ▁techniques ▁such ▁as ▁tree ▁ring ▁d ating ▁or ▁carbon - 1 4 ▁dates , ▁help ▁ref ine ▁the ▁regional ▁curves . ▁ ▁Te chni que ▁A ▁number ▁of ▁samples ▁are ▁removed ▁from ▁the ▁feature ▁by ▁enc as ement ▁in ▁non - mag net ic ▁pl aster ▁within ▁non - mag net ic ▁m ould s . ▁ ▁These ▁samples ▁are ▁marked ▁for ▁true ▁north ▁at ▁the ▁time ▁of ▁collection . ▁ ▁The ▁samples ▁are ▁sent ▁to ▁an ▁Arch ae om agnet ic ▁Labor atory ▁for ▁processing . ▁▁ ▁Each ▁of ▁the ▁samples ▁is ▁measured ▁in ▁a ▁sp inner ▁magnet ometer ▁to ▁determine ▁the ▁thermal