# Comparisons
source: https://developer.mastercard.com/carbon-calculator/documentation/use-cases/engagement-services/comparisons/index.md

The **Comparisons** service provides a comparison of CO2 emissions in tonnes with everyday life examples.

It provides relatable examples to help users better understand their environmental impact.

## Pre-requisites {#pre-requisites}

There are no pre-requisites for the issuer to use this service.
Tip: To create your project on Mastercard Developers, refer to the [Before You Start](https://developer.mastercard.com/carbon-calculator/documentation/index.md#before-you-start) section for more information.

## Sequence Diagram {#sequence-diagram}

The following sequence diagram shows the order of events for a solution that uses the `/comparisons` endpoint.

Diagram engagement-comparisons

### User journey {#user-journey}

1. The consumer requests the issuer app to get the comparison.
2. The issuer app sends the comparison requests to the issuer server.
3. The issuer server sends the comparison request to the Carbon Calculator app.
4. The Carbon Calculator app validates the request and fetches a random comparison based on the parameters provided, if any.
5. If the request is invalid, the Carbon Calculator app returns an error response for an invalid request or any missing request parameter to the consumer.
6. The issuer server returns the comparison to the issuer app.
7. The issuer app returns the comparison to the consumer.

Note: For more information about the error codes, refer to [Code and Formats](https://developer.mastercard.com/carbon-calculator/documentation/code-and-formats/index.md).

## Endpoint {#endpoint}


API Reference: `GET /comparisons`