# The azimuth pointer/scribe mark

There is a scribe mark on a plate on the fixed part of the platform where the azimuth (gregorian side) equals 270 degrees.
• a retractable  pointer is mounted on the encoder platform (gregorian size).
• When the azimuth encoder reads 270 degrees, the pointer should align with the scribe mark.
• this was developed to recover the azimuth position whenever an encoder problem arose.
• If we have an encoder problem:
• move the pointer to the scribe mark and then reset the encoder to 270 degrees.
• We can probably reset the position to about 1/64". at the 60 foot radius of the scribe mark this is about 1.2 milliDeg, or about 4asecs.
• The system is calibrated using the pointing model.. the sequence is:
• before a new pointing model is made
• move the azimuth to 270 degrees (using no pointing model corrections.. just use the preset command on the vertex console).
• Make sure the pointer is aligned with the scribe mark
• If it is not aligned:
• move the pointer to the scribe mark
• reset the encoder to 270
• Take a picture of the pointer,scribe mark for later reference.
• Make the new pointing  model.
• If the pointer / scribeMark was not pointing at true 270 degrees, the pointing model will correct for it.

# Pictures of aligning the az pointer with the scribe mark

• 23jan12: encoder 1 becomes loose.
• 22jun15: encoder 1 fails. replaced on 23jun16.
• the picture includes a metric ruler
• 01oct16: encoder 1 replaced
• pictures taken after new encoder aligned at az=270
• 11sep19: corrected az encoder 1 jump by 1 tooth
• has before and after pictures
• It includes a ruler to show the offset distance.
• The jump occurred on 12aug19
• 16oct19. The az encoder 1 jumped by 1 tooth.
• There is only an after alignment picture.
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