It looks like the units are set within the custom transformer as a parameter with an alias.

You can edit the definition of the parameter.

Within the configuration section, you can add a new choice with an alias. An alias would be the number of seconds in a month or year. I assume this wasn't included as the number of seconds in a month or year vary and therefore any output wouldn't be accurate.

see topic yesterday..

[clock format [clock scan today] -format {%j}] - [clock format [clock scan {YourAttribute}] -format {%j}]

(difference compared to today..)

replace %j (for days of year) with %W (for weeks of year) to get weekdifference.

To calculate daydifference over years ( over yearboundaries) you need to check if year is a leapyear

Or do clock scan and then use one of common calculations.

The DateTimeCalculator in 2017 allows you to do this quite easily

If you can't upgrade to FME 2017 just yet, here's a quick Python solution for a PythonCaller. Expects the input attributes "start_date" and "end_date" on the format YYYYMMDD, outputs the attribute "difference_in_years":

from dateutil.relativedelta import relativedelta
from datetime import datetime

def CalculateYearsElapsed(feature):
    start_date_str = feature.getAttribute("start_date")
    end_date_str = feature.getAttribute("end_date")
    start_date = datetime.strptime(start_date_str, '%Y%m%d')
    end_date = datetime.strptime(end_date_str, '%Y%m%d')
    difference_in_years = relativedelta(end_date, start_date).years
    feature.setAttribute("difference_in_years", difference_in_years)

Thank you for your help. It runs.