1. Structure: inside and outside the two-tier structure, the inner layer is two fixed writing boards flush with the front of the whiteboard, the outer two sliding writing board. 2. Basic dimensions: ≥4000mm × 1300mm (4000mm × 1350mm), can be adjusted according to the whiteboard feature, ensure effective support and whiteboard. 3. Writing board: high quality paint steel, thickness ≥0.3mm. Dark green matte board, film hardness 6H, roughness Ra1.6-3.2um. The core material: high strength, sound-absorbing, moisture-proof, fire-retardant polystyrene board, thickness ≥13mm. 5. Back: high quality matt painted steel rustproof, every 8 cm with 2 cm reinforce groove. 6. Cover plate: using environmentally friendly two-component polyurethane glue, automated assembly line sheathing job (the job-site pictures), proper bonding board formation, formaldehyde emission ≤0.2mg / L, in line with GB / T 28231-2011 "Writing board safety and health requirements." 7. Border: horizontal frame size ≥100 × 57mm, mullion size ≥29 mm × 100 mm, frame by oxidation, sandblasting coating, no glare; horizontal (vertical) box with double reinforcement structure, thick ≥10 mm. 8. Pulley: The hanging round double slide, next slide flat round single structure, sliding smoothly, low noise; when writing the exact location is not shaking, shaking back and forth sliding plate is less than 0.5mm. 9. Dust tank: with integrated dust groove width ≥30mm prevent dust vertical landing; dust tank and bottom border integration of design, no dust sweeping corners; chalk and other tools in order to prevent falling, there is one of the dust and the dust tank cleanup tools, when not, can replace the dust plugs to block dust holes. 10. corners material: anti-aging high-strength ABS plastic injection molding, double-walled chamber into a sleek design, rounded ≥R25mm, with a registered trademark. 11. Limit file: blackboard inside the border on both sides of the sliding plate installation file limit, prevent impact activities blackboard box is turned upright. 12. The products should comply with GB / T 28231-2011 "writing board safety and health requirements" and GB 21027-2007 "General requirements for safety school supplies" and other national standards, and provide above the level of inspection reports issued by the Technical Supervision.