One fact, two clocks
One day, read with both clocks
Where the first clock comes from
3 Mar · Price agreed
The price takes effect in the world. That is the first clock.
True, not yet known
The new price is in force, and nothing on record says so yet.
20 Mar · On record
The memory records it. That is the second clock.
One fact, two clocks
17 days a single clock cannot see
Bi-temporal memory
Two dates on every fact.
First clock · Valid time
The first clock: when it was true
Second clock · Knowledge time
The second clock: when it was known
One clock
17 days a single clock cannot see
As it stood on 10 Mar
A week after the price was agreed, ten days before anyone recorded it.
First clock · Valid time
True on 10 March: the new price.
Second clock · Knowledge time
On record on 10 March: the old price.
History
The earlier entry is kept and marked as replaced.
A quote sent on 10 March
At the price on record that day. Not a mistake.
Stated by the source
When a source says when something takes effect, that date is the first clock.
No date in the source
The fact counts from the moment it was recorded.
Learn
Bi-temporal memory.
One fact, two clocks
3 Mar · Price agreed
The price takes effect in the world. That is the first clock.
True, not yet known
The new price is in force, and nothing on record says so yet.
20 Mar · On record
The memory records it. That is the second clock.
One fact, two clocks
17 days a single clock cannot see
Timer's two clocks: when something was true in the world, and when your organization knew it.
01 The Definition
Two dates on every fact.
Bi-temporal memory
Two dates on every fact.
noun · data modelling
Bi-temporal memory
Bi-temporal memory records every fact against two separate timelines: when it was true in the world, known in data modelling as valid time, and when the organization came to know it, known as transaction or knowledge time. Timer calls these its two clocks and applies them to an organization's decisions, commitments and agreements rather than to rows in a database.
The difference matters whenever the two dates diverge. A price is agreed on 3 March but only reaches the finance team on 20 March. A policy is reversed in May, yet the memo that announced it still reads as current. With both clocks, the memory can be read as it stood on any past date: what was true, what the organization knew at that moment, and what replaced it later. A correction adds to the record instead of overwriting it, so the question an auditor, a board or a new hire actually asks, "what did we know when we decided?", has an answer on the record rather than in someone's recollection.
Timer, 2026.
withtimer.com/bi-temporal-memory#definition
02 The Two Clocks
One fact, two dates. Most records keep one of them, and overwrite it.
First clock · Valid time
The first clock: when it was true
Second clock · Knowledge time
The second clock: when it was known
One clock
17 days a single clock cannot see
- C1The first clock: when it was true Valid time. The date something took effect in the world: the day a price was agreed, a policy came into force, a commitment was made. It belongs to the event, whoever wrote it down and whenever they did.
- C2The second clock: when it was known Knowledge time, also called transaction time. The moment the organization's memory first recorded the fact. It belongs to the record, and it is what lets any past day be read as it stood.
A record with one clock keeps the latest value and the moment it was saved. It cannot tell a price that changed on 3 March from one the organization only heard about on 20 March, and it cannot tell either from a mistake corrected a week later. Those are three different events, and after the fact each one answers a different question.
03 Bi-temporal Truth
Read the record as it stood. Three answers about one day, not one.
As it stood on 10 Mar
A week after the price was agreed, ten days before anyone recorded it.
First clock · Valid time
True on 10 March: the new price.
Second clock · Knowledge time
On record on 10 March: the old price.
History
The earlier entry is kept and marked as replaced.
A quote sent on 10 March
At the price on record that day. Not a mistake.
Take 10 March: a week after the price was agreed, ten days before anyone recorded it. With both clocks, the memory answers three different questions about that day.
- Q1What was true on 10 March? The new price. It was agreed on 3 March, so by the first clock it was already in force.
- Q2What was on record on 10 March? The old price. The new one reached the record on 20 March, so by the second clock nobody could have acted on it yet.
- Q3What replaced it later? Whatever superseded it afterwards, and when. The earlier entry is kept and marked as replaced, never overwritten.
Bi-temporal truth is holding the first two answers at once and being able to show the third. It is what makes a past decision fair to judge. A quote sent on 10 March at the old price was not a mistake: the old price was what the organization had on record that day. One clock cannot show that. Two can.
04 Where The Dates Come From
The first clock is only as good as its source.
Stated by the source
When a source says when something takes effect, that date is the first clock.
No date in the source
The fact counts from the moment it was recorded.
The second clock belongs to the memory: it is the moment a fact was first recorded. The first clock has to come from somewhere. When a source states when something takes effect (a contract's start date, the day a policy applies from, the date a decision was made), that date is the first clock.
When a source does not say, Timer does not guess. The fact counts from the moment it was recorded, the one date that can be stood behind. An invented effective date is worse than none, because it arrives with a citation attached, and a citation is what stops a reader checking.
05 Questions
Asked about the two clocks.
What is bi-temporal memory?
Bi-temporal memory records every fact against two separate timelines: when it was true in the world, known in data modelling as valid time, and when the organization came to know it, known as transaction or knowledge time. Timer calls these its two clocks and applies them to an organization's decisions, commitments and agreements rather than to rows in a database.
What is the difference between valid time and transaction time?
Valid time is when a fact was true in the world. Transaction time, also called knowledge time, is when it was recorded. A contract signed on 1 June and filed on 9 June has a valid time of 1 June and a transaction time of 9 June. A bi-temporal record keeps both, so it can answer a question about either.
What are Timer's two clocks?
Timer's name for the two dates every fact in its memory carries: when it took effect in the world, and when the organization's memory first recorded it. Both travel with the fact, including into an export of the memory.
What is bi-temporal truth?
The ability to answer two different questions about the same day: what was true then, and what the organization knew then. A past decision can only be judged fairly against the second. Timer's memory keeps both, so "what did we know when we decided?" is answered from the record rather than from recollection.
Does a correction overwrite the original fact?
No. A correction is added to the record and the original is kept, marked as replaced. The memory can still show what the organization believed before the correction, when that changed, and what it changed to.
Is bi-temporal modelling new?
No. Valid time and transaction time have been established in data modelling for decades, in the systems that keep financial, legal and regulatory records, and the SQL standard has defined temporal tables since 2011. The idea is not Timer's. What Timer does is apply it to an organization's memory, to what it decided, promised and agreed, rather than to the tables of a single application.
Why does bi-temporal memory matter for AI?
An AI reading a memory with one clock can only report the latest value, and it presents today's answer as if it had always been true. With both clocks it can answer a question about March from what was on record in March, and say what changed afterwards and when. People and the AI systems working for the organization read the same record, with the same two clocks.
Get started
The future belongs to organizations that remember.
For companies of 50 people or more.