In the hierarchy box for the WebDewey record for **500 Natural science and mathematics**, there appear at first glance to be three different entries for the number **500**:

A closer look reveals that the **50**0 just above the entry for **500 Natural science and mathematics** has the last zero grayed out, and only **50** is in blue and underlined as a link. The **5**00 at the top has both zeros grayed out, and only the **5** is in blue and underlined as a link. Why? The three different entries are used to display different hierarchical relationships. In the hierarchy box for the WebDewey record for **500 Natural science and mathematics** shown above, the entries in the downward hierarchy all have the format **500.X**: **500.2**, **500.5**, and **500.8**. In the bar at the top of the hierarchy box, the focal notation is displayed as **500**. That notation matches the notation in the 153 field of the underlying MARC record (click the MARC button to see the underlying record):

153 ## 500 $e 50 $j Natural sciences and mathematics

In the hierarchy box, click the entry just above the record for **500 Natural science and mathematics**, and the downward hierarchy in the format **50X** will be displayed:

In the bar at the top of the hierarchy box, the focal notation is displayed without the grayed-out zero: **50**. That notation matches the notation in the underlying MARC record:

153 ## 50 $e 5 $j Science

Click the top entry inside the hierarchy box, and the downward hierarchy in the format **5X0** will be displayed:

In the bar at the top of the hierarchy box, the focal notation is displayed without the grayed-out zeros: **5**. That notation matches the notation in the underlying MARC record:

153 ## 5 $j Science

Why do the two entries with grayed-out zeros have a shortened caption—Science—by comparison with the full caption for **500**: Natural science and mathematics? The captions for entries with grayed-out zeros come from DDC Summaries: "The headings associated with the numbers in the summaries have been edited for browsing purposes and may not match the complete headings found in the schedules."

Like entries in DDC Summaries, the entries for numbers with grayed-out zeros have no notes, no Relative Index entries, and no mapped terminology.

What about number-span entries, e.g., **580-590 Natural history of plants and animals** in the hierarchy box for **5 Science** above? There are no number-span entries in DDC Summaries, and no modified headings for them. The zeros are not grayed out, and clicking that entry in the hierarchy box leads to the full record with notes.

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