The Metropolitan Museum of Art holds a clay tablet 10.3 by 5.3 centimeters, about the size of a deck of cards. The museum catalogs it as a "balanced account of Dugga," Neo-Sumerian, about 2039 BC. It came to New York in 1911 (accession 11.217.3).
An account of this kind has one job. It lists what came in and what went out, and it closes to a balance. It is worth keeping only if it reads the same on the day it is checked as on the day it was written.
A Book You Can Edit Is a Draft
A lender reads the books. An auditor reads them. So does the board that takes office next spring. Each assumes the page in front of them is the page that was written.
If an entry can change without a trace, that assumption is the whole risk. The book stays a draft until someone proves otherwise.
What Immutable Means in the Ledger
Three things, and each can be checked.
A decision, once written, is not edited. Every entry passes one enforcement point before it exists, where the guards that apply to it evaluate it. The decision is written before the entry and again after. Each decision's hash includes the one before it, and every night the chain is recomputed and sealed into a snapshot.
A posted entry is not edited. A mistake is corrected by a new entry that reverses it. Both stay on the record, with who made the correction and when.
The rules that matter most are held in the database as well as in the application.
What It Does Not Do
Immutable does not mean right. A wrong entry stays on the record, and so does its correction. The person who reads the books next sees both.
Check It
The counts are public, with a digest that covers them: communitypay.us/verify/platform.
Years later, the entry can still be examined.
Scott Vuilleumier · Founder of CommunityPay, Inc.
Data science, investment banking, and financial systems engineering and ledger design.