This is all to do with
use of reference lines ... a reference line simply allows you to adjust the
'calculation' for a further condition ... and when using reference lines, we
ALWAYS GO TO THE REF LINE FIRST, then adjust to the condition ... so for this problem:
1. Enter on the base
scale at 450nm ... up to the ref line ... make a pencil mark.
2. Follow 'adjustment
curve' back down till you meet the condition '50kt tail', make a pencil mark.
3. Now vertically up to
the next section .... 45000kg Landing weight ... make a pencil mark.
4. Now across to the
right hand scale .... 2500kg of fuel required.
.... remember,
always to the ref line first, then adjust to the condition.