Under “Days/year” you specify the number of days to be used each year to estimate the hourly day type patterns. The period is centred around the forecast start date, 1, 2, 3, etc. years back. The exception is the same year in which the forecast starts, as half a period is used the current year before the forecast start, if not ‘Number of years back is set to 0’. In that case, the whole period is used.