Factbox on Pak presidential election Pakistan's presidential election on Saturday is not a popular vote but a ballot of the country's two houses of parliament and four provincial assemblies. Three candidates are contesting the election, which was prompted by the resignation of Pervez Musharraf in the face of impeachment charges last month. The frontrunner is Asif Ali Zardari, the widower of former prime minister Benazir Bhutto, who represents the Pakistan People's Party (PPP). He is being challenged by retired chief justice Saeed-uz-Zaman Siddiqui, backed by former prime minister Nawaz Sharif, and Mushahid Hussain, a close aide of Musharraf. Here are some key facts about the election. -- The president will be voted in by an electoral college comprising the 342-seat National Assembly and the 100-seat Senate, as well as members of the country's four provincial assemblies in Punjab, Sindh, North West Frontier Province and Baluchistan. -- Voting is by secret ballot. It starts at 10:00 am (0400 GMT) and closes at 3:00 pm. --- Musharraf resigned August 18 over threats of his impeachment and Sharif withdrew backing from Pakistan's coalition government one week later over a dispute with Zardari on the reinstatement of judges sacked by the former president. -- Zardari is expected to win easily because the PPP and its allies have an overall majority in the assemblies. -- Zardari became co-chairman of the PPP after the assassination of Bhutto in a suicide attack in December 2007. Here are some key facts about the powers of the president. -- Controversial changes by former military ruler Musharraf made to the constitution empower the president to sack the prime minister, his government and to dissolve the elected parliament. -- The president is the supreme commander of the armed forces and also has the power to appoint chiefs of the three services, provincial governors, the chairman of the election commission and the attorney general. -- The president also enjoys the power to waive capital punishment and pardon any condemned prisoner. Political events in Pak since Musharraf sacked CJ Pakistani lawmakers will in a secret ballot Saturday choose a successor to former president Pervez Musharraf, who resigned last month under threat of impeachment. Here follow the main political events in Pakistan since Musharraf sacked the country's chief justice in March 2007, an event widely seen as pivotal to him eventually leaving office. -- 2007 -- March 9: Musharraf sacks chief justice Iftikhar Muhammad Chaudhry, sparking protests. Chaudhry reinstated by Supreme Court in July. July 10: Pakistani troops storm the radical Red Mosque in Islamabad, killing scores. October 6: Parliament elects Musharraf to another five-year term as president in a vote boycotted by the opposition. October 18: Former premier Benazir Bhutto returns from exile. November 3: Musharraf imposes state of emergency, sacks chief justice, suspends constitution. November 25: Former premier Nawaz Sharif returns from exile. November 28: Musharraf steps down as army chief and hands control of military to General Ashfaq Kayani December 15: Musharraf lifts state of emergency. December 27: Bhutto assassinated at election rally. -- 2008 -- February 18: Parties of Bhutto and Sharif trounce Musharraf's allies in general elections. March 24: Parliament elects Bhutto aide Yousuf Raza Gilani as prime minister. July 29: Thousands of demonstrators in Karachi hail arrival of former chief justice Chaudhry. August 7: Coalition says Musharraf to face impeachment. August 17: Coalition says it has finalised impeachment charges. August 18: Musharraf announces his resignation. Aug 21: At least 64 people killed in a double suicide attack near Islamabad, the deadliest this year. Aug 23: Asif Ali Zardari, the widower of Benazir Bhutto, decides to stand for the presidency. Aug 25: The government outlaws militant group Tehreek-e-Taliban Pakistan (TTP). Aug 25: Sharif's party quits Pakistan's ruling coalition over differences on the reinstatement of the judges sacked by Musharraf. August 29: Zardari moves house amid fears of attacks being made on his life. September 3: Snipers fire at Prime Minister Gilani's motorcade in a failed assassination attempt