# Live monitoring during a test
Story: “I sit on console during a test and watch live telemetry from the system in front of me. I want every channel on screen, and calculations that still work on units that record fewer channels.”
This page is for engineers who watch a test or an operation as it happens, such as an operator who wants a live view of every [channel](https://dev.nominal.io/platform/reference/glossary.md#channel "A named signal: a series of measurements or computed values, such as voltage, pressure, or system state.") on the unit in front of them, or an analyst who adds calculations on top of that telemetry.
## Live monitoring prerequisites
Live monitoring works from a unit’s [asset](https://dev.nominal.io/platform/reference/glossary.md#asset "A physical or simulated device or system you track in Nominal, such as a vehicle, a component, a unit under test, or a test stand."), because an operator watches a physical unit. Each unit you monitor needs an asset. If your units don’t have assets yet, start from [Organize and view your data](https://dev.nominal.io/platform/data-model/paradigms.md).
One [workbook template](https://dev.nominal.io/platform/reference/glossary.md#template "A workbook saved without a run or asset, so the same analysis can be applied to each new run or asset.") works on every asset that uses the same [ref name](https://dev.nominal.io/platform/reference/glossary.md#ref-name "The name an asset or run gives each data source attached to it, such as default. Workbooks and checklists find channels by ref name and channel name."), such as `default`.
```mermaid
---
config:
layout: elk
---
flowchart BT
classDef green fill:#dcfce7,stroke:#15803d,color:#1f2937
classDef blue fill:#e0f2fe,stroke:#0369a1,color:#1f2937
asset1["Asset: UUT1"]:::green
asset2["Asset: UUT2"]:::green
template["Workbook template
Console layout
Looks for `default`.(channel)"]:::blue
workbook1["Live workbook
UUT1"]:::blue
workbook2["Live workbook
UUT2"]:::blue
asset1 --> workbook1
asset2 --> workbook2
template -.->|"new workbook from template"| workbook1
template -.->|"new workbook from template"| workbook2
click asset1,asset2 href "../../../#asset" "Asset"
click template href "../../../../../quickstart/quick/quick-template/" "Workbook templates"
click workbook1,workbook2 href "../../../../workbooks/#live-workbooks" "Live workbooks"
```
## Walkthrough: live monitoring
### Stream data to Nominal
[Stream](https://dev.nominal.io/platform/reference/glossary.md#stream "To send points to Nominal as they're produced, instead of uploading a finished file.") or upload data from your test system into each asset’s dataset with a client library or connector. If the units share a dataset, tag each point with an identifier.
### Build the workbook template for your console
1. In the sidebar, click **Assets** and open one unit’s asset.
2. Click **NEW WORKBOOK**. A new [workbook](https://dev.nominal.io/platform/reference/glossary.md#workbook "Where you analyze time-series data from assets and runs, in tabs and panels, after a test or live.") opens as a blank canvas.
3. In the **CHANNELS** section of the **Channels & variables** sidebar, type to filter the channels. Select the ones you want with the checkboxes, or with Ctrl/Cmd-click and Shift-click.
4. Drag the selection onto the canvas to create a time series chart. Drag more channels onto an existing chart to plot them all together.
5. Save the layout as a template: open the workbook menu (the logo ▾ at the top left), then choose **File** ▸ **New template**. In the template editor, preview it against an asset, then click **PUBLISH**, enter a **Message**, and click **PUBLISH**.
### Create a workbook instance for each unit under test
1. Open the unit’s asset.
2. Click the arrow beside **NEW WORKBOOK** and choose **New workbook from template**.
3. Pick your console template.
### Go live
1. In the bottom bar, click **GO LIVE**. The button reads **LIVE** while the workbook streams. Click it again to stop.
2. Choose a [time window](https://dev.nominal.io/platform/reference/glossary.md#time-window "The time range currently shown in a workbook. It controls what data Nominal loads and updates when you zoom or pan.") from the dropdown beside it. The default is the last 30 seconds.
**GO LIVE** isn’t available if the workbook has [time offsets](https://dev.nominal.io/platform/reference/glossary.md#offset "A time shift applied to data without changing its stored timestamps."), if all of its runs have ended, or if its [data source](https://dev.nominal.io/platform/reference/glossary.md#data-source "Anything an asset or run reads time-series data from: a dataset, a connection to an external database, or a video.") can’t stream, such as an external database [connection](https://dev.nominal.io/platform/reference/glossary.md#connection-nominal-data-source "A data source that links to an external time-series database, so Nominal can read data from outside systems.").
Once a test is complete, you can mark its time bounds with a [run](https://dev.nominal.io/platform/reference/glossary.md#run "A named, time-bounded period of interest on one or more assets, such as a test, a flight, or a race session.") for later review.
## Walkthrough: adding analysis
### How does analysis work in Nominal?
A workbook doesn’t plot channels directly. Instead, data on a chart is a [variable](https://dev.nominal.io/platform/reference/glossary.md#variable "A reference to a channel, with any tag filters, splits, and transforms applied, or a formula built from other variables. Workbooks plot variables, and checklists check them."), which refers to a channel plus any [transformation](https://dev.nominal.io/platform/reference/glossary.md#transform "An operation that builds a new time series from an existing one, such as a rate of change or a unit conversion, without changing the original data.") or manipulation of that channel’s raw data. Plotting a channel always creates a variable with no transformation.
Every variable has a [variable name](https://dev.nominal.io/platform/reference/glossary.md#variable-name "A variable's unique identifier in a workbook, such as aa, which formulas use to refer to it.") and a display name. The variable name, such as `aa`, `ab`, or `ac`, is the variable’s unique identifier in the workbook, and [formulas](https://dev.nominal.io/platform/reference/glossary.md#formula "An expression, such as a + b, that computes a new time series from existing numeric variables in a workbook or checklist.") use it. The display name defaults to the channel’s name and appears in charts and legends. Variables reference their channel by [ref name](https://dev.nominal.io/platform/reference/glossary.md#ref-name "The name an asset or run gives each data source attached to it, such as default. Workbooks and checklists find channels by ref name and channel name.") and channel name, written `default.voltage`, rather than by dataset, so the same workbook and formulas work on every asset that uses that ref name.
```mermaid
---
config:
layout: elk
---
flowchart RL
classDef purple fill:#e0e7ff,stroke:#4338ca,color:#1f2937
classDef blue fill:#e0f2fe,stroke:#0369a1,color:#1f2937
subgraph dataset1["Dataset: UUT1"]
voltage["Channel: voltage"]:::purple
current["Channel: current"]:::purple
end
style dataset1 fill:#f5f7ff,stroke:#4338ca,color:#1f2937
subgraph workbook1["Workbook"]
aa["Variable aa
Display name: voltage
Points to: default.voltage"]:::blue
ab["Variable ab
Display name: current
Points to: default.current"]:::blue
ac["Variable ac
Display name: power
Formula: aa * ab"]:::blue
chart["Chart"]:::blue
end
style workbook1 fill:#f0f9ff,stroke:#0369a1,color:#1f2937
aa --> voltage
ab --> current
ac --> aa
ac --> ab
chart --> aa
chart --> ac
click dataset1,voltage,current href "../../../#time-series-data" "Time-series data"
click aa,ab,ac href "../../../../reference/glossary/#variable" "Variable"
```
The transformations permitted by a variable include filtering a channel by tags, splitting data by tag, and performing general math functions over the data in a channel, such as unit conversion or time derivatives. A formula is a variable built from other variables, such as `ac` above, which multiplies `aa` and `ab`.
The **Custom formula** window has its own reference which shows supported operators and the available variables with their variable names and display names.
A formula’s inputs don’t need to be recorded at the same rate. The output of the formula uses the first variable in the formula as a timing source. Each other input contributes its most recent point from up to 1 second before. Where another input has no point in that second, the formula has no value. To override this default, you can deliberately [🔒︎resample](https://docs.nominal.io/core/documentation/platform/transforms/time-domain-transforms#resample) the inputs to a common interval first.
#### When a unit doesn’t record a channel
When an asset lacks a channel that a workbook uses, only the variables that reference that channel, and formulas built on them, stop plotting for that asset. The rest of the workbook keeps working, and the affected legend entries show a warning:
### Add calculations to the template
Add calculations to the console template, so every new workbook made from it gets them.
1. In the sidebar, click **Workbooks**, then the **Templates** tab, and open your console template. A published template is read-only: click **EDIT TEMPLATE**, enter a name under **New draft**, and click **NEW DRAFT**.
2. Preview the draft against one unit’s asset, so channel search lists that unit’s channels.
3. Add the channels the calculation uses as [variables](https://dev.nominal.io/platform/reference/glossary.md#variable "A reference to a channel, with any tag filters, splits, and transforms applied, or a formula built from other variables. Workbooks plot variables, and checklists check them."), by plotting them or adding them from channel search.
4. In the **VARIABLES** section, click **+** and choose **Custom formula**.
5. Enter a **Name** and an **Expression**, using the variable names listed under **VARIABLES**. For example, `sqrt(aa**2 + ab**2)`.
6. Click **ADD FORMULA**.
7. Click **PUBLISH**, choose **Publish as latest version…**, enter a **Message**, and click **PUBLISH**. The draft’s changes don’t reach the template until you do.
Workbooks already made from the template keep their old layout. To add the calculation to one, follow the steps below.
### Add calculations to one workbook
Add a calculation to one unit’s workbook to try it out, to give it to that unit only, or to add it to a workbook made before the template changed. It doesn’t change the template or any other workbook.
1. Add the channels the calculation uses to the workbook as [variables](https://dev.nominal.io/platform/reference/glossary.md#variable "A reference to a channel, with any tag filters, splits, and transforms applied, or a formula built from other variables. Workbooks plot variables, and checklists check them."), by plotting them or adding them from channel search.
2. In the **VARIABLES** section, click **+** and choose **Custom formula**.
3. Enter a **Name** and an **Expression**, using the variable names listed under **VARIABLES**. For example, `sqrt(aa**2 + ab**2)`.
4. Click **ADD FORMULA**.
## Next steps
- [Repeatable test execution](https://dev.nominal.io/platform/data-model/paradigms/stories/repeatable-runs.md): record each test as a run and compare runs afterwards.
- [Automated pass/fail checks](https://dev.nominal.io/platform/data-model/paradigms/stories/automated-checks.md): have [checks](https://dev.nominal.io/platform/reference/glossary.md#check "A rule that evaluates time-series data against a condition, such as a threshold or a state change, and creates an event wherever the condition is met.") flag problems as the data arrives.