Anushtup Chandaha -- Meaning?

We always read "anushtup chandaha" in the beginning of Sanskrit hymns. What does it mean?

By specifying this in the beginning, it is made clear how to read the given line. It gives a hint to the reader/chanter where or which word to stress more and where to not stress more while reading. This is way to minimize error in reading and to improve the effectiveness of the text which is being read.

• It actually means eight syllables in a quarter. 
• There are several metres defined in Sanskrit texts. For ex: 
• Metres with 4 syllables in a quarter are called "pratishta".
• Metres with 5 syllables in a quarter are called "supratishta".
• Metres with 6 syllables in a quarter are called "gayathri".
• Metres with 7 syllables in a quarter are called "ushnik".
• Metres with 8 syllables in a quarter are called "anushtup".
• Metres with 9 syllables in a quarter are called "vruhathi".

Let's take a simple example to understand the usage of this metric. Consider the following mantra:

vakratunda mahakaaya suryakoti samaprabah:

nirvighnam kuru me deva sarva karyeshu sarvada

Applying "Anushtup" Metre or Metres with 8 syllables in a quarter, we can read the above mantra as:

| vak | ra | tun | da | ma | ha | ka | ya| (8)

  | sur| ya | ko | ti | sa | ma | pra| bha| (8)

  |nir | vigh | nam | ku | ru | me | de | va (8)

  |sar | va | kar | ye | shu| sar| va | da | (8)