# How to correctly specify the time window within which the fluid balance applies

**Category:** [Ask IEB](https://discourse.openehr.org/c/ask-ieb/37)
**Created:** 2024-07-10 16:44 UTC
**Views:** 48
**Replies:** 1
**URL:** https://discourse.openehr.org/t/how-to-correctly-specify-the-time-window-within-which-the-fluid-balance-applies/5451

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## Post #1 by @Lucas

**Unimportant Context but interesting:**
For the use case assessing a patient's fluid balance, I decided to use the archetype OBSERVATION.fluid_balance.v1 - no surprise so far ;-). But the surprise came step-by-step. In the clinical knowledge manager the archetype is depicted as follow

![image|690x241](upload://qFx1E6wuXP3RrOUMvyu0aAd8eI2.png)

But if I go to the archetype designer to check the archetype fluid balance, then it looks very different, namely

![image|407x468](upload://isCU9dsqPMfSmYfpOaY7dYsmhC5.png)

And if I add this archetype to a composition, it looks different again, namely

![image|351x499](upload://pK4Rkb4bYQD6SyyHuYnvW40uPGf.png)

**Important Context:**
But my biggest surprise came, when I wanted to test the "Any interval event" by uploading the template in the Form Builder by Better. The template simply consists of the COMPOSITION.report-result.v1 which includes the archetype OBSERVATION.fluid_balance.v1.  But when testing it, I had no option to define an arbitrary time interval for the attribute "Any interval event".

**My question:**
* Is there a way to define an arbitrary time interval, such as from DD.MM.YYYY:HH:MM until DD.MM.YYYY:HH:MM, only by relying on the archetype OBSERVATION.fluid_balance.v1? 
* If not, is there a way to include the attributes "from" and "until" as DD.MM.YYYY:HH:MM without resorting on specialization of this archetype or bloating it with the Timing archetypes?

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## Post #2 by @Lucas

I tinkered with the template and realized, that there are attributes inherited by the reference model to actually instantiate an arbitrary time window using the following attributes:

![image|690x448](upload://wIgSQSf1rOtXeqMFhkNjNmp6ej8.jpeg)

Unfortunately, I was unable to expose this possibility in the Form Builder provided as Sandbox by Better - thank you Better for your support.  But fortunately, I now know, that this can be instantiated by other means.
 
And I also figured out what format is expected for the attribute offset, namely (copied and pasted from https://www.digi.com/resources/documentation/digidocs/90001488-13/reference/r_iso_8601_duration_format.htm)

> P(n)Y(n)M(n)DT(n)H(n)M(n)S

Where:

* **P** is the duration designator (referred to as "period"), and is always placed at the beginning of the duration.
* **Y** is the year designator that follows the value for the number of years.
* **M** is the month designator that follows the value for the number of months.
* **W** is the week designator that follows the value for the number of weeks.
* **D** is the day designator that follows the value for the number of days.
* **T** is the time designator that precedes the time components.
* **H** is the hour designator that follows the value for the number of hours.
* **M** is the minute designator that follows the value for the number of minutes.
* **S** is the second designator that follows the value for the number of seconds.

For example:

> P3Y6M4DT12H30M5S

Represents a duration of three years, six months, four days, twelve hours, thirty minutes, and five seconds.

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**Canonical:** https://discourse.openehr.org/t/how-to-correctly-specify-the-time-window-within-which-the-fluid-balance-applies/5451
**Original content:** https://discourse.openehr.org/t/how-to-correctly-specify-the-time-window-within-which-the-fluid-balance-applies/5451