Student Rulers Professional acrylic rigid plastic scale rulers for all your flight planning needs. CSR-124CM ( 1:250,000 & 1:500,000 ) CSR-242CM ( 1:250,000 & 1:500,000 ) CSR-342CM ( 1:500,000 & 1:1,000,000 ) CSR-432CM ( 1:500,000 & 1:1,000,000 ) CSR-642CM ( 1:1,000,000 & 1:500,000 ) KSR156'' & 15CM Stainless Steel Ruler NPR4040CM & 16''