A Letter of Attestation is required by a number of EU Member States. The following is taken from ec.europa.eu:
A form attesting activities of a driver with a view to ensure compliance with drivers' hours rules was established by Decision 2009/959/EU amending Decision 2007/230/EC. This form comes only in addition to the tachograph records and should reflect activities which could not be recorded via tachograph due to technical reasons.
Member States are not obliged to require the use of this form, but if a form is required, this form will be recognised valid for such purposes.
Using the data you already enter in to Tachomaster it is able to generate attestation letters that cover days not recorded on to the tachograph, such as: Annual Leave, Sick days, days worked without driving. It is also possible to print a Letter of Attestation and fill in the activity yourself.
Start by searching for a Worker using the search field in the main menu. When you have found the worker locate the section labelled "Recent Activity":
Click the "Print Attestation of Activites" button to continue.
The following screen contains the required fields for the attestation letter. Check each field, some of which will be pre-populated where possible.
The last section on the form consists of a From and To date range and a checkbox:
Select the From and To date you are wanting to cover with an attestation of activities.
To have Tachomaster automatically create attestation letters for the given period leave the checkbox empty. If you would like a single letter printed with no activity selected, check the box.
Click "Generate Attestation Letters" to create the letters