Route distance on basecamp is different in gps

Have you looked at the detail of the routes by comparing them in BaseCamp with your device connected? Are you sure they are identical? If they are I'm surprised the mileage on your device is double what it says in BaseCamp. Are you sure its not adding the distance from where you are to the start of your route?

I'd expect to see minor variations but not what you're experiencing 

I'm pretty far from the route, so it can't be the latter. Can you tell me how to compare them?

It shouldn’t be too hard to determine which one is correct.

Especially if it’s so much larger on the GPS “every time”.

Try a third route planner. 

You can compare them by just looking at both of them in BaseCamp. If they appear identical open up the route properties and see what distance is shown there. You should also be able to see visually in BaseCamp whether a route is 4 or 8 miles 

He’s sending the route from BaseCamp. They are likely going to look the same.

In any case, it should be easy to determine which of these are correct.

I wonder if the BaseCamp distance is the sum of the strait line distances between waypoints. The GPS may be providing the distance along the calculated path.

They do appear the same. When I look at both routes in Basecamp, the distances are the same. But when I unplug the device and look at the route on it, that's when the distance is different. The route still looks the same on the device. 

Which one is (more) correct?

Is it always longer on the device?

The device, so far, has always said it's longer. I've only used the gps once on a hike. Sorry, I just got it. But the hike that I did take, Basecamp distance was 6.3 and gps said it was 7.9. After completing the hike I was at about 7.3. 

It's less confusing to stick with one example. Keep in mind that only you can see anything.

The difference between 4.47mi in basecamp and 8.82mi is very large. It should be easy to determine which of these is more correct.