---
title: "Useful Sinclair Programmer Notes: Telephone Number Compression Program"
type: "article"
slug: "useful-sinclair-programmer-notes-telephone-number-compression-program"
url: "http://localhost/article/useful-sinclair-programmer-notes-telephone-number-compression-program/"
markdown_url: "http://localhost/article/useful-sinclair-programmer-notes-telephone-number-compression-program.md"
published_at: "2026-03-15T01:17:57+00:00"
modified_at: "2026-03-15T01:17:57+00:00"
featured_image:
  url: "http://localhost/wp-content/uploads/2022/04/20230809-041332.jpg"
excerpt: "Continuation of the Amateur Programmers' Line column exploring a technique for packing 7-digit telephone numbers into 3 bytes of ZX-81/TS1000 RAM. Discusses the encoding strategy, edge cases (leading zeros, digit groups exceeding 255, null/empty numbers requiring reserved codes), and variable-length field design for memory-constrained database applications on orphan computers. Includes a short BASIC type-in program…"
category:
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  - name: "Type-in program"
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model:
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indiv:
  - name: "Bill Harmer"
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publication_r:
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  title: "TS Bulletin"
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authors_r:
  - name: "Bill Harmer"
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issue: "7"
issues_articles:
  - id: 33992
    title: "TS Bulletin S-7-90"
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    url: "http://localhost/issue/ts-bulletin-s-7-90/"
pages: "4"
pubdate: "September 1990"
archive_link: false
---

Continuation of the Amateur Programmers’ Line column exploring a technique for packing 7-digit telephone numbers into 3 bytes of ZX-81/TS1000 RAM. Discusses the encoding strategy, edge cases (leading zeros, digit groups exceeding 255, null/empty numbers requiring reserved codes), and variable-length field design for memory-constrained database applications on orphan computers. Includes a short BASIC type-in program demonstrating POKE-based storage and PEEK-based retrieval of a sample phone number using fixed RAM addresses from 16523 upward.