I wrote recently about Kibana’s excellent Timelion feature, which brings time-series visualisations to Kibana. In the comments Ben Huang asked:

do you know how to show whats the difference between this Friday and last Friday by Timelion?

So I thought I’d answer properly here.

Timelion includes mathematical functions including `add`

and `subtract`

, as well as the ability to show data `offset`

by an amount of time. So to answer Ben’s query, we combine the two.

First, our starter series, simply showing a count of all documents across all indices:

```
.es()
```

Now let’s check out the `offset`

function, showing the same data but for the previous week:

```
.es(offset=-1w)
```

We can combine the two on the same chart:

```
.es(*),.es(offset=-1w)
```

And then we can subtract one from the other:

```
.es().subtract(.es(offset=-1w))
```

Tarting it up a bit, we can show all three series, adding `label`

for each, and formatting the difference series as bars instead of lines clearly to identify it better:

```
.es().label("Original"),.es(offset=-1w).label("One week offset"),.es().subtract(.es(offset=-1w)).label("Difference").bars()
```

Mucking about with the `lines`

syntax, setting a `fill`

and zero-`width`

lines, we can show bars but with width of each data point (1 day):

```
.es().label("Original"),.es(offset=-1w).label("One week offset"),.es().subtract(.es(offset=-1w)).label("Difference").lines(steps=1,fill=2,width=0)
```

So there you have it - the difference calculation between two time points in Timelion, with a bit of formatting fun thrown in for a bonus.