what is part serial number in last sir means

It means the serial number of your name in the electoral roll for that particular part number or polling-booth area. In simple terms, the part number shows the booth/list area, and the serial number shows your position in that list.

Simple example

• Part number = which polling booth or section your record belongs to.
• Serial number = your row number in that section’s voter list.

In “SIR” forms

In the Special Intensive Revision voter records, these details are used to identify your exact entry in the roll, and they are usually printed in the voter list or linked records.

What to check

• Look for Part No.
• Look for Serial No.
• If the form says “part serial number” , it is usually referring to both details together, not one single thing.

A clearer wording

If someone says “part serial number,” they usually mean:

Part number + serial number in the voter list.

TL;DR: Part number = polling booth/list section; serial number = your number inside that section.