Tipping Point: What is a constant maturity gilt fund?

What is a constant maturity gilt fund? 

In most categories of funds, fund managers have the leeway to alter the average duration of the fund, based on their interest rate outlook. When interest rates are expected to fall, they increase the average duration of their fund, and vice versa. But sometimes, fund managers can get their duration calls wrong. They may increase the average duration of their fund in anticipation of a decline in interest rates, but rates may harden instead.

Constant maturity gilt funds guard against the risk of wrong duration calls by fund managers. These funds keep their average duration