The question from Mark is:
By "the description" you mean the wording
日歩4銭也の割合 , right?
Why do you believe that this wording "leave absolutely
no possibility of compounding"?
Please, give some evidence for your assertion.
Does 日歩 always refer to only simple interest?
If so, how did you come to know this?
I looked up 日歩 in a dictionary, whose definition
was silent about the issue of whether the amount
of interest each day is added to the principal so that
the principal for calculating the second day's amount
of interest is greater than the principal for calculating
the first day's amount of interest -- i.e., whether the
interest is simple or compounded.
-- Mark Spahn (West Seneca, NY)
It is purely the context that leaves no doubt. As Katy said, this is a description of a lease, not a loan. The lease has an exact amount, and that is what the penalty is assessed against, at the rate of JPY0.04 per JPY100. The amount of the lease does not change because you accumulate penalties. There just isn't any ambiguity in the Japanese wording, but you introduce ambiguities when you start talking percentages. Don't think of this as an interest rate, but rather as a penalty for late payment.