Several features are incorporated for easier location of the specimen and idenfication of areas of special interest.

• Referring to the annular rim indentifies north, south, east and west.

• The four quadrant markers are tapered towards the centre.

• 100 Radial sectors are easily identified by reference to decimal number in the annular rim and alphabet letters in the four quadrants.

• A matt surface on one side is for correct position - matt side up.