The X, Y and Z label pointers are placeholders for any one of the SRGraphLabelBlock (or derived) objects. The axis drawing system will normally assign a semi-permanent label block (SRGraphLabelBlock) or decimal scale (SRGDecimalScale) to one of these pointers for the duration of its existence. Keeping the same label block and modifying it requires far less time than constantly creating and destroying large, complex objects on the stack.