3 OP already strike off these paragraph. Delete it to make it easier to read.
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Countdown is more than the "60", "30 seconds", 10,9...1 we see on TV, or hear on the PA adjacent to the launch site. Countdown commences well before the launch date with regular checkpoints for various systems and parts on the schedule as Thomas Tarrants mentions in his answer. It is also a process that may be forked - more on that below.

In addition to verification countdown also allows resolution of issues identified. Say diagnostics on system X report an error at T-24 Hours. The error may be of such a nature as not to interfere with the rest of the systems. Then the system owner for X may recommend continuing verification (countdown till T-23 Hours i.e. 1 hour to identify, and fix the fault) to hold at T-23 Hours.

The transcript of the Gemini III mission is available at the link below http://www.jsc.nasa.gov/history/mission_trans/gemini3.htm

There are other mission transcripts available on the same page which might make interesting reading as they present a picture of the countdown as it proceeds. Just click on 'Choose', and select the mission of your choice.

This page on the NASA site explains how countdowns work - http://www.nasa.gov/mission_pages/shuttle/launch/countdown101.html

Remember that the rocket/spacecraft looks to us laymen to be a monolith; In reality it is thousands of parts, and systems working together.

Countdown is more than the "60", "30 seconds", 10,9...1 we see on TV, or hear on the PA adjacent to the launch site. Countdown commences well before the launch date with regular checkpoints for various systems and parts on the schedule as Thomas Tarrants mentions in his answer. It is also a process that may be forked - more on that below.

In addition to verification countdown also allows resolution of issues identified. Say diagnostics on system X report an error at T-24 Hours. The error may be of such a nature as not to interfere with the rest of the systems. Then the system owner for X may recommend continuing verification (countdown till T-23 Hours i.e. 1 hour to identify, and fix the fault) to hold at T-23 Hours.

The transcript of the Gemini III mission is available at the link below http://www.jsc.nasa.gov/history/mission_trans/gemini3.htm

There are other mission transcripts available on the same page which might make interesting reading as they present a picture of the countdown as it proceeds. Just click on 'Choose', and select the mission of your choice.

This page on the NASA site explains how countdowns work - http://www.nasa.gov/mission_pages/shuttle/launch/countdown101.html

Remember that the rocket/spacecraft looks to us laymen to be a monolith; In reality it is thousands of parts, and systems working together.

Countdown is more than the "60", "30 seconds", 10,9...1 we see on TV, or hear on the PA adjacent to the launch site. Countdown commences well before the launch date with regular checkpoints for various systems and parts on the schedule as Thomas Tarrants mentions in his answer. It is also a process that may be forked - more on that below.

In addition to verification countdown also allows resolution of issues identified. Say diagnostics on system X report an error at T-24 Hours. The error may be of such a nature as not to interfere with the rest of the systems. Then the system owner for X may recommend continuing verification (countdown till T-23 Hours i.e. 1 hour to identify, and fix the fault) to hold at T-23 Hours.

This page on the NASA site explains how countdowns work - http://www.nasa.gov/mission_pages/shuttle/launch/countdown101.html

Remember that the rocket/spacecraft looks to us laymen to be a monolith; In reality it is thousands of parts, and systems working together.

2 Provided a link better suited to the question
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Countdown is more than the "60", "30 seconds", 10,9...1 we see on TV, or hear on the PA adjacent to the launch site. Countdown commences well before the launch date with regular checkpoints for various systems and parts on the schedule as Thomas Tarrants mentions in his answer. It is also a process that may be forked - more on that below.

In addition to verification countdown also allows resolution of issues identified. Say diagnostics on system X report an error at T-24 Hours. The error may be of such a nature as not to interfere with the rest of the systems. Then the system owner for X may recommend continuing verification (countdown till T-23 Hours i.e. 1 hour to identify, and fix the fault) to hold at T-23 Hours.

The transcript of the Gemini III mission is available at the link below http://www.jsc.nasa.gov/history/mission_trans/gemini3.htm

The transcript of the Gemini III mission is available at the link below http://www.jsc.nasa.gov/history/mission_trans/gemini3.htm

There are other mission transcripts available on the same page which might make interesting reading as they present a picture of the countdown as it proceeds. Just click on 'Choose', and select the mission of your choice.

There are other mission transcripts available on the sameThis page which might make interesting reading as they present a picture of the countdown as it proceeds. Just click on 'Choose', and select the mission of your choice.NASA site explains how countdowns work - http://www.nasa.gov/mission_pages/shuttle/launch/countdown101.html

Remember that the rocket/spacecraft looks to us laymen to be a monolith; In reality it is thousands of parts, and systems working together.

Countdown is more than the "60", "30 seconds", 10,9...1 we see on TV, or hear on the PA adjacent to the launch site. Countdown commences well before the launch date with regular checkpoints for various systems and parts on the schedule as Thomas Tarrants mentions in his answer. It is also a process that may be forked - more on that below.

In addition to verification countdown also allows resolution of issues identified. Say diagnostics on system X report an error at T-24 Hours. The error may be of such a nature as not to interfere with the rest of the systems. Then the system owner for X may recommend continuing verification (countdown till T-23 Hours i.e. 1 hour to identify, and fix the fault) to hold at T-23 Hours.

The transcript of the Gemini III mission is available at the link below http://www.jsc.nasa.gov/history/mission_trans/gemini3.htm

There are other mission transcripts available on the same page which might make interesting reading as they present a picture of the countdown as it proceeds. Just click on 'Choose', and select the mission of your choice.

Remember that the rocket/spacecraft looks to us laymen to be a monolith; In reality it is thousands of parts, and systems working together.

Countdown is more than the "60", "30 seconds", 10,9...1 we see on TV, or hear on the PA adjacent to the launch site. Countdown commences well before the launch date with regular checkpoints for various systems and parts on the schedule as Thomas Tarrants mentions in his answer. It is also a process that may be forked - more on that below.

In addition to verification countdown also allows resolution of issues identified. Say diagnostics on system X report an error at T-24 Hours. The error may be of such a nature as not to interfere with the rest of the systems. Then the system owner for X may recommend continuing verification (countdown till T-23 Hours i.e. 1 hour to identify, and fix the fault) to hold at T-23 Hours.

The transcript of the Gemini III mission is available at the link below http://www.jsc.nasa.gov/history/mission_trans/gemini3.htm

There are other mission transcripts available on the same page which might make interesting reading as they present a picture of the countdown as it proceeds. Just click on 'Choose', and select the mission of your choice.

This page on the NASA site explains how countdowns work - http://www.nasa.gov/mission_pages/shuttle/launch/countdown101.html

Remember that the rocket/spacecraft looks to us laymen to be a monolith; In reality it is thousands of parts, and systems working together.

1
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Countdown is more than the "60", "30 seconds", 10,9...1 we see on TV, or hear on the PA adjacent to the launch site. Countdown commences well before the launch date with regular checkpoints for various systems and parts on the schedule as Thomas Tarrants mentions in his answer. It is also a process that may be forked - more on that below.

In addition to verification countdown also allows resolution of issues identified. Say diagnostics on system X report an error at T-24 Hours. The error may be of such a nature as not to interfere with the rest of the systems. Then the system owner for X may recommend continuing verification (countdown till T-23 Hours i.e. 1 hour to identify, and fix the fault) to hold at T-23 Hours.

The transcript of the Gemini III mission is available at the link below http://www.jsc.nasa.gov/history/mission_trans/gemini3.htm

There are other mission transcripts available on the same page which might make interesting reading as they present a picture of the countdown as it proceeds. Just click on 'Choose', and select the mission of your choice.

Remember that the rocket/spacecraft looks to us laymen to be a monolith; In reality it is thousands of parts, and systems working together.