interval on x-axis and y-axis values

Hi there,
I am using NCL 5.0 and trying to plot an xy plot with user defined
interval on x-axis and y-axis. For example if the minimum and maximum
values on x-axis are 20 and 30 respectively and i want an interval of 2
which means values on x-axis should 20, 22, 24 .. 30. How can i tell
NCL to use this user defined interval.

Regards,

-- 
---
Basit A. Khan
PhD Candidate
Centre for Atmospheric Research
Department of Geography
University of Canterbury  Te Whare Wananga o Waitaha Private Bag 4800 
Christchurch 8020, New Zealand
Tel: (643) 364 2987 Ext. 7912
Fax: (643) 364 2907
bak41_at_student.canterbury.ac.nz 
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