I've put a new chain on my bike using method 3 from Zinn's art of road bike maintenance to determine length:
"Wrap the chain around the big chainring and biggest cog without going through either dérailleur. Bring the two ends together until the ends overlap; one full link (Fig. 4.7) should be the amount of overlap (Fig. 4.10)..."
However, I didn't notice that my fingers must have slipped at some point because I remeasured the size after breaking the surplus pieces off & the overlap was gone (facepalmed myself with a greasy hand at this point).
How big of an issue is this likely to be? What are the problems associated with an overshortened chain? Realistically, should I be running down to the bike shop and buying a second chain in as many days (whilst trying to pretend I hadn't)?
I rarely (if ever, I dislike cross-chaining) end up on both the big cogs and chainring at the same time therefore the chain & rear dérailleur would rarely be under maximum possible tension. I'm aware it's not a good idea to re-add links and given I'm about to head to the Alps I don't want a weak chain!