The ladder, as a strategy

What does rolling a maturing rung do to a ladder's length?

• Keeps it, because a new rung is added at the far end
• Shortens it, because a rung has matured
• Doubles it, because the money is reinvested

Rates have fallen since you built your ladder. What happens to its average locked yield when you roll one rung?

• It drops straight to the new rate
• It moves toward the new rate by that one rung's share
• It stays the same until every rung has matured