In the SX editor and Loan/Mortgage Druid, there is an assumption about american-style mortgage rates 
that makes using the "official" rate given by any canadian bank difficult if you don't know how to do the 
math. The reason is that posted Canadian rates for mortgages are compounded semi-annually, 
although the actual interest itself is compounded monthly or biweekly or whatever based on your 
payment period.
There is a way to convert the canadian loan to an effective periodic rate, just as a US rate is simply 
divided by the number of periods. However, this is compicated and non intuitive to the end-user.

On the long run, it would be good to actually improve the SX Editor/Druid so that it can generate the 
proper formulas by itself, but a first step is to add basic scheme code so that users can manually enter 
the needed formula if required.

I also have issues with rounding where the two components of a mortgage repayment (Int+Principal) 
don't match the payment, typically by one cent.