I have to smile at the range of opinions I am getting here. Some posters are telling me not to micromanage the nanny, and others are telling me to go measure her tires 
There are apps that track miles drivenspecifically for situations like this.
Have you driven the one logical best route in your own car to see how it compares with both Google Maps and her claims?
I just looked up the distance of a route I walk frequently. Using Google Maps directions shows 1.3 miles. Measuring exactly the same route by its individual segments comes out to 1.47 miles. That’s a pretty big difference for such a short distance.
Computer inaccuracy % is worse for short distances.
For longer distances its better as you are driving down a single highway … accuracy % much better for main highways… as the highways are defined more accurately and anyway you stay straighter for longer.
That said, the vehicles odometer might be 10% out , due to the tyres being 10% different circumference to what the odometer/spedometer are calibrated to.
Since we now know we’re dealing with rural Switzerland. …
Google’s estimates of shorter routes will have a larger percentage error than will longer routes.
Google’s estimates of twisty curvy routes will have a larger percentage error than will straighter routes.
Google’s estimates of hilly routes will have a larger percentage error than will flatter routes.
Google’s estimates of routes on small minor roads will have a larger percentage error than will routes on major roads.
Google’s estimates of routes over multiple intersecting roads will have a larger percentage error than will routes on a single road.
All of these are results of quantization errors and simplifications in their map data and their software.
I’d bet the OP’s cases are probably mostly on the increased error side of each of these factors. That plus a slightly flaky odometer could easily be worth 10%.
An intellectually honest approach by the OP is to drive the common routes once himself and compare his odometer readings to Googles’. Any systematic bias should be pretty obvious.
Actually for the short twisty trips from one remote mountain valley to another I just have the nanny strap the kids onto one of our goats :rolleyes:
In fact, the area we live in is pretty flat and straight, and most of the trips in question include the autoroute (highway).
I agree it is a good idea to test this with my own car. I just did this for the most common trip she takes, from home to school. My car’s odometer told me the trip was 15.4 kilometers, Google said 15.7 km, and my nanny claims it is 17. Make of it what you may…
Have her odometer calibrated. Or yours.
Who knew Switzerland was so modern and civilized! I’d imagine it to be like the movie Heidi.
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I don’t know the rate for Swiss, but I know the common rates recommended for Germany, three levels: for friends in the Alpine Club, recommended is 0.10 Euros per kilometer (traditionally measured by the odomoter, since you are all sitting in the same car, and easier than paying for a big gas tank of 70 liters back in the days)
what the tax office re-imbursed people traveling to / from work, which is adjusted regularly, and last I looked, somewhere around 0.50 and 0.70 Euros per km
What the ADAC (Auto club) calculates, using maintenance, deprecation, insurance, and is much higher than what the tax office uses.
The current cost of gas is a small part of the cost per km.
That’s when the driving is not part of the job, but getting to/ from the job.
But if the nanny is taking the kids, she is chauffering them, so it’s paid time, plus the expenses for the car itself.
Are the trips the same week for week, month to month? Because you say you originally wanted to save the Nanny the hassle of keeping a log; but now you are mistrusting her because of what Google tells you.
If the activities and hence the routes are the same every week, just let her keep a log for one or two weeks, and then use that. No constant hassle for her, no mistrust from you.
Look at what your country’s car club recommends for mileage costs, and round up since she is taking care of the kids while in the car.
Google gets you to the destination. It doesn’t include parking lots, parking garages, private roads, having to go around obstructions and detours, etc… One example: I go to my friend’s ritzy county club. Google maps says that I have arrived. It’s another 1.5 miles on a private gated road to the actual clubhouse. Guest parking is probably another .2 miles. (A cart picks you up at your car).
How much is she over your estimate? 5% is nothing.
Orville would like to apologize for not getting back to you sooner, but he is stuck on an important business yodel.
The GQ level answer seems to have been arrived at as best it can be. Two individual cars’ odometers varied by about 10% (or look at as the average +/- 5%) … assuming her 17 was a precise number and not a rounded one … and Google was closer to their average.
From your own small dataset we know that car odometers may commonly vary at least +/- 5% from some hypothetical true number. We have no independent verification of Google’s estimate but its being in between the two odometer readings does make it seem more likely the most accurate of the bunch.
So now what do you do with that? That’s not GQ.
It comes to what? A bit less than $40 bucks a month.
- Offer her the alternate option to keep a log and trust it and her odometer which seems to be reading high, maybe leaving you feeling like you are being stiffed $40/month but what you would have done if you hadn’t been trying to save her the hassle of keeping the log.
- Tell her that her odometer is wrong and that we go by Google, leaving her feeling like she’s being stiffed the $40/month.
- Spring for one of those apps kayaker linked to. They’re pretty cheap to free. Odds are after a week of using it and seeing for herself that they concur with Google she’ll just accept the Google numbers.
Option two seems the poorest choice even though the facts may be on your side but that’s IMHO territory.
Thanks DSeid. Very well-summarised.
I will probably let her decide between 1 and 2. Although I personally like 3, knowing my nanny, she would start complaining about the cost of the data usage for the app and ask us to pay for her entire monthly phone subscription. She really does niggle us for every cent, which I guess is partly why I am obsessing a bit too much about the mileage thing. By that would definitely go into IMHO territory!