I have a Vesper system as well, but prefer
Anchor Alert running on Android.
Once the chain is out, I enter the length deployed, adding a bit to account for
helm position being further back. Then here's the good part ....
While applying
power in reverse to set the
anchor, I point the
phone to it. The app uses the phone's
compass and
GPS to calculate the anchor position. When I'm satisfied the anchor is set, I press OK on the app and can now rest easy. There is an independent field to enter the acceptable movement outside the circle before alarming. The display shows where the
boat has drifted within the swing circle.
On the downside, I almost abandoned this app because it woke me occasionally with false alarms due to losing
GPS signal in the
cabin. Since swapping phones (to inexpensive Sony Xperia M), it has not failed once in several months' of use.
Battery usage is a bit heavy, consuming about 60% of a full
battery overnight. So I plan to install a USB
charger downstairs and keep it plugged in all night.
A couple of features I have not used are an exclusion zone, and automated alert to another
phone so if you are ashore and the anchor drags it will call you.