# Re: time unit in CF-netCDF

```Benno,

```
How to write time-bounds in the time value and unit? Mike told me to best use scale factor and offset to convert a period to "day" (i.e., "3 days 1 hours and 5 minutes" = 0.3283922462941847 "day"). This solves the non-standard period issue. If time bounds can be used, it will also allow a time variable to contain time durations of different lengths.
```
Wenli

At 15:13 2007-6-29 -0400, Benno Blumenthal wrote:
```
To be CF compliant, you should write the units in days and use time-bounds to set the edges of the (irregular) intervals. the attribute unit must be in udunits -- P4D is not or P 4 day are not acceptable.
```

Benno

Wenli Yang wrote:

```
```Hi,

```
How to express the unit of an irregular period of time in the time coordinate variable in CF-netCDF? For example, for two 4-day periods: a) between 2007-01-01 and 2007-01-04; and b) between 2007-01-05 to 2007-01-08, which of the followings are correct?
```    1. time(time)=1,2       unit = "P 4 day since 2007-01-01"
2. time(time)=1,2       unit = "P4D since 2007-01-01"

```
There are names for regular time periods, such as week and fortnight, in udunits.dat. For irregular time period, such as 3 days 1 hours and 5 minutes, I am not sure if we should use ISO 8601 expression, "P1M3DT1H5M" or something like "P 1 month 3 day 1 hour 5 minute" as unit.
```
Thanks.

Wenli

```
===============================================================================
```To unsubscribe thredds, visit:
http://www.unidata.ucar.edu/mailing-list-delete-form.html
```
===============================================================================
```
```
```

==============================================================================
To unsubscribe thredds, visit:
http://www.unidata.ucar.edu/mailing-list-delete-form.html
==============================================================================

```
• 2007 messages navigation, sorted by:
• Search the `thredds` archives: