Example 1:

We want to observe a target at 12:15:00 +54:55:00 for 100 ksec.  
The histogram plot for RA=183Deg, Dec=+55deg says that there is a total of
793.8 ksec available.  Our request is less than 25% of the available time, 
and there is 344 ksec available in 4 windows each longer than 30 ksec (note
that, in order to make the histogram plots readable, all windows longer than 30
ksec are plotted in the 30 ksec bin).  This observation should not pose any
significant scheduling difficulties.


Example 2:


We want to observe a target at 01:50:00 +50:32:00 for 100 ksec.
The histogram plot for RA=28Deg, Dec=+50deg says that there is a total of
419.4 ksec available.  That is more than 4x100 ksec, so we're OK with the 25% 
rule.  However, the available windows are all much smaller than 100 ksec and 
since the four largest windows only add up to 66 ksec (2*18+16+14) it will 
take more than 4 visits to accomplish the observation.


Example 3:

We want to observe a target at 06:55:00 +45:01:00 for 50 ksec.  The 
histogram plot for RA=104.1deg, Dec+45deg, shows that there is a total
estimated exposure time of 194 ksec available - less than 4x50.  Also the four 
largest windows sum up to only about 48 ksec (14+2*12+10).  Hence such an 
observation would require both more than four separate visits and would 
require that all, or most, of the longest opportunities be utilized.  The 
observation would have to be given very high priority to have a reasonable 
likelihood to be accomplished.