Start with a fixed routine

It works best if your calculation is "verifiable" from the start: always the same type of data, the same way of recording, and an outcome that you can directly find later. Then, "where does this amount come from?" is not a quest through emails, photos, and loose notes.

At Autotelex, we therefore choose an approach where input and output together form a small dossier. Think of vehicle data (model or variant, fuel, transmission, body type), the CO2 value with source (for example, WLTP or NEDC, depending on what applies to the car), the dates used (first admission and the date on which the calculation was made), and the value basis (why that value fits this car). It is also handy to supplement this with a screenshot of the input and a PDF of the output. This way, you can directly return to "this was the set of data" later, without having to puzzle again.

The input where it usually goes wrong

Differences usually arise not from one button, but from a few input fields that you rush through. With fixed checks, your calculation remains not only quick but also easy to explain.

Reference date is one of them. It helps if you consciously choose which date makes sense for your process, instead of automatically taking "today". What often works well: one standard date as a fixed basis, and possibly a second scenario for moments when you are still in the process. Then you can also immediately see later why two amounts are stored and which amount belongs to which moment.

Then execution and CO2. Here you want execution and CO2 to be recorded as one whole, including a brief source citation. A simple check: you should be able to see in one sentence where the CO2 comes from and that it belongs to this execution. For example: "CO2 taken from source X, belongs to execution Y." If that is stored directly, your input remains consistent and you don't have to guess later how the value was established.

And then value and worth. It helps if you briefly note why that value makes sense for this car, plus what it is based on. Any special features (such as signs of use or unusual options) should be noted there immediately. This way, you prevent only seeing an amount later without context.

Quick calculation or verifiable calculation: what fits your moment?

Quick calculation is handy in the orientation phase: you quickly have a direction and can compare more easily. Just make sure to save the outcome as an indication, including the input used, so you can see exactly what you calculated later. Verifiable calculation takes a few extra minutes, but it makes it easier to answer questions without having to figure everything out again.

Depreciation and valuation: when it's better to work more specialized

Sometimes it is not straightforward, for example with unusual executions, unclear vehicle data, or discussions about the condition. Then it helps if your dossier becomes heavier: more substantiation, more context, and a calculation that remains easy to follow. You will notice that this is especially needed when it is not clearly visible which execution and vehicle data were used, or if the condition of the car makes a visible difference in value. Then it is handy if your calculation can be directly linked to additional substantiation, such as a valuation report, so that there is not only an amount but also a document to refer to.