Not 100% sure, but I can see a few different ways. One is what you described - just using the last weigh-in. Another depends on the graph - sometimes it is better to leave them blank than feed them potentially misleading information. At least blank, when you look back months later, reminds you that you were away and didn't have your scale available.
What I'd probably do is record the numbers the other scale gave, but pay more attention to the difference day to day while there. Then when I returned I would go back and adjust them based on the apparent difference.
For example, just making up some numbers:
Home - 172
Day 1 - 180
Day 2 - 181
Day 3 - 179
Day 4 - 180
Day 5 - 182
Day 6 - 178
Home - 169
I see about an 8 to 9 pound difference between the scales at home and away, so I might subtract 8 from each of the away weights (so day 1 would end up 172, day 2 would be 173, and so on). This works best after the fact - but could be frustrating if you don't like seeing the higher number or if the change from Home to Day 1 is notably different from Day 6 to Home.
Have a marvelous time no matter what you decide.
| current weight: 179.5