Hi, can someone please help with me with the following:

I have an old book on sundial which dates to the pre-calculator age, which contains formulas I need to have in my java program to write a visual sundial designer. Now the problem is i cant understand some of the equations as my maths is a bit rusty.

the first equation is

log tan SD = log sin T + log cot P ...

where SD is a value that needs to be found, T and P are arbitrary values.
I have been able to work out SD like this .. SD = ArcTangent( Sin T * Cot P)
which gives me the right answer .. .

now im stuck with the following equation:

log cot DL = log cot T + log sin P

i dont how to find dl for the above equation can someone plz provide me some tips .. id really appreciate it iv been stuck trying to solve this for 3 days ..