<prompt> Translate the following text to EnglishUharibifu wa thamani kama sehemu ya Pato la Taifa umeongezeka kidogo katika miongo minne iliyopita, na akiba ya kitaifa ya usawa - ambayo haijumuishi uharibifu - bado iko chini ya wastani wa miaka ya 1960, kama inavyoonyeshwa katika takwimu.  <response>: Depreciation as a share of GDP has increased slightly over the past 4 decades, and net national saving-which excludes depreciation-remains well below the 1960s average, as shown in figure 