# Logging Logging allows signal data to be saved without message data bytes and IDs. The Logging screen (Figure 1) is accessed from the **Measurement** menu. ![Figure 1: The Logging screen.](/files/AIYJ33iUD8JJckNG6I1z) ### Selecting a Signal Group Logging uses the same signal groups as the [Signal Plot](/vspy-3-documentation/vehicle-spy-main-menus/main-menu-measurement/signal-views/signal-plot.md) and [Signal List](/vspy-3-documentation/vehicle-spy-main-menus/main-menu-measurement/signal-views/signal-list.md) features (Figure 1:![](https://cdn.intrepidcs.net/support/VehicleSpy/assets/smOne.gif)). Start by choosing the desired signal group via the **Signal Group to Log** drop-down list. To change the signals in that group, click on **Select Signals**. The ![](https://cdn.intrepidcs.net/support/VehicleSpy/assets/logging_+.gif) and ![](https://cdn.intrepidcs.net/support/VehicleSpy/assets/logging_-.gif) buttons can be used to add and remove signal groups. You can also press the **Copy Selected Group** button (![](https://cdn.intrepidcs.net/support/VehicleSpy/assets/logging_copy.gif)) to duplicate the currently-selected signal group. ### Enabling Logging Enable the Logging feature for the selected signal group by clicking the checkmark next to **Log This Signal Group** (Figure 1:![](https://cdn.intrepidcs.net/support/VehicleSpy/assets/smTwo.gif)). This will activate most of the other controls in the window. ### Logging Status and Data While Logging is active, its status is shown in the upper right corner (Figure 1:![](https://cdn.intrepidcs.net/support/VehicleSpy/assets/smThree.gif)). You can view data as it is being collected by pressing the **View Data** button. ### Logging Setup This option area sets primary parameters for logging (Figure 1:![](https://cdn.intrepidcs.net/support/VehicleSpy/assets/smFour.gif)). These are the options found in this area: * **Log at Constant Rate / Log All Updates:** Determines whether all data is logged or it is instead time-sampled. Choosing **Log All Updates** will disable the **Log Rate** options below. * **Log Rate (sec/sample):** The frequency at which data is sampled and logged. * **Save when data changes only:** When enabled, new entries are created only when data changes; this can help reduce storage requirements. * **Log File:** The name of the file where data is to be stored. * **Log File Creation Options:** Specifies when to reuse existing log files or start new ones, and under what circumstances. * **Ignore formatting on signals and save as analog values:** When checked, analog values are saved without the specified formatting setup for the signal. * **Write CSV File / Write MDF File:** The file format for saving data; at least one must be checked. ### Start Logging The parameters in this area (Figure 1:![](https://cdn.intrepidcs.net/support/VehicleSpy/assets/smFive.gif)) dictate when Vehicle Spy begins logging data. The two options are: * **Start Automatically:** Logging begins immediately when Vehicle Spy starts. * **Start on Equation:** Vehicle Spy begins logging when the defined condition evaluates as **True**. Selecting this option enables the equation button (![](https://cdn.intrepidcs.net/support/VehicleSpy/assets/Functionbutton.gif)), which you can click to select the start condition using the [Expression Builder](/vspy-3-documentation/shared-features-in-vehicle-spy/shared-features-expression-builder.md). The **Enable Pre Start Collection** option allows the capture of a number of seconds of data immediately preceding the start trigger. ### Stop Logging Choose an option in this box (Figure 1:![](https://cdn.intrepidcs.net/support/VehicleSpy/assets/smSix.gif)) to tell Vehicle Spy when logging should stop: * **Stop Automatically:** Logging stops when Vehicle Spy does. * **Stop on Equation:** Vehicle Spy stops logging when the defined condition evaluates as **True**. As with the start condition, you can click ![](https://cdn.intrepidcs.net/support/VehicleSpy/assets/Functionbutton.gif) to specify the stop condition. * **Stop After a specific amount of time:** Logging stops after a specified number of seconds. The **Zip file when stopped** option tells VSpy to compress the logged data in a zip file to save space. ### Invalid Signal Handling An invalid signal can occur when signal data is cleared in a function block, or when Vehicle Spy starts before signal data is available. The program offers several options to deal with such conditions (Figure 1:![](https://cdn.intrepidcs.net/support/VehicleSpy/assets/smSeven.gif)): use the last value, leave the value blank, or replace the invalid value with one specified in the **Replace with Value** field. This last option is handy if other programs are going to chart or graph this data; blank or text entries can be replaced with a value that is still able to be graphed, but is known to be invalid, so it is not confused with valid data. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.intrepidcs.com/vspy-3-documentation/vehicle-spy-main-menus/main-menu-measurement/logging.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.