有一个apt-get的翻译问题不明白

hyperslaver

update
          update is used to resynchronize the package index files from their
          sources. The indexes of available packages are fetched from the
          location(s) specified in /etc/apt/sources.list. For example, when
          using a Debian archive, this command retrieves and scans the
          Packages.gz files, so that information about new and updated
          packages is available. An update should always be performed before
          an upgrade or dist-upgrade. Please be aware that the overall
          progress meter will be incorrect as the size of the package files
          cannot be known in advance.
最后一句:
'An update should always be performed before
          an upgrade or dist-upgrade. Please be aware that the overall
          progress meter will be incorrect as the size of the package files
          cannot be known in advance.
不太明白,前面都懂.

springwind426

简单地说

就是在用apt-get 安装软件的时候，需要先运行一下update，使本地记录的软件信息与数据仓库中的软件信息同步。

aerofox

在 upgrade 或 dist-upgrade 操作之前总是应该执行 update 操作。请注意，由于包文件大小不能事先知道，所以总进度条可能不正确。

hyperslaver

Post by aerofox;1794473
在 upgrade 或 dist-upgrade 操作之前总是应该执行 update 操作。请注意，由于包文件大小不能事先知道，所以总进度条可能不正确。

我不明白的是
overall progress meter
的意思
现在明白了,是进度条的作用.

因此,谢谢各位的热心帮助