... * Precision, 60'+/-9' * The black ring is 5mm in diameter * Color,blue& red * Material,acrylic * Name, precision measuring* Item No.,RB-SV2006 ... , * Color,purple,blue,red and so on* The precision is 60'+/-10',the air bubble will be always at the middle ... your requirements(size,precision and so on) High precision level RB-SV2006