DualCalc > Additional Tools

Currently available ...

The following packages of tools are currenly available:

    DOS Tools

    Second version, released 4 December 2005

    Actually the name is a bit confusing, they are actually Windows programs but they look like DOS programs on-screen and contain the code of some of the programs from the old DOS package amended to work under Windows as an add-in to DualCalc.

    This package contains 'Schedule' a scheduler, 'Builder' a schedule builder and a 'Multical' a 'what if?' multi-calculator.

    Please download the installer, then run it and point the destination to the folder in which you keep DualCalc.  The tools should be installed next time you run DualCalc.

    Once installed, if you are not familiar with the old DOS package, please select the 'Read instructions' options (in Schedule this is in the 'Facilities Menu' and in Multical, help is available by keying F1) and read both the General Instruction and the instructions specific to the individual programs.


    Analyse is the first 'serious' Windows based add-in for DualCalc.  It provides a sort of 'what if?' calculator where you can fill in the known information and ask Analyse to calculate an unknown.  Analyse duplicates or enhances the functions of 'Multical' (one of the DOS add-ins, see above) so, although MultiCal remain available, you may want to consider removing it when you download and install Analyse.  Click here for more information.


    Note, the 'Period' Windows add-in, previously available here, is being incorporated into DualCalc as an input tool and has therefore been withdrawn.

    Card Total

    Second version (1.4), released 17 December 2005

    This illustrates that a DualCalc tool doesn't have to be written in BBC Basic for Windows.  The question it deals with is the effect the amount you pay each month on a credit card has on how long have to keep paying and how much interest you pay in total.  This package installs a tool written in HTML and JavaScript which allows the user to enter different repayment amounts and examine the effect.

    Please download the .zip, then save the contents in the Tools folder inside the folder in which you keep DualCalc.  The tool should be installed and available next time you run DualCalc.

    This version corrects an error which allows users to enter a repayment amount of zero or less and provides an additional check for users who enter a very small repayment which eventually falls below the amount of interest charged (making the account run forever).

    Incidentally, the code from this page is also being used by the OFT as part of their 'be sensible with your credit card over the Christmas 2006 period' campaign.

    As the interface is as simple as possible, it's not really apparent what the program in this page is doing and it's not as straightforward as some of the other JavaScript calculators, so a few people have asked how it works:

    Basically, because the repayments under a card agreement are often controlled by the minimum repayment rate rule (eg you must may a repayment equal to at least 3% of the balance), they keep changing every month.  Then, at some point, the minimum repayment amount rule (eg you must pay at least £5 a month, if that's bigger than the minimum repayment rate), or the amount the borrower chooses to repay every month, kicks in and the repayments stay at that level.

    This makes it difficult to come up with a formula to calculate how long the balance takes to pay off.  An easier approach is to simply work through the loan a month at a time, recalculating the balance each time until it pays off - that's what the page does.  The algorithm is something like this (incidentally, the following doesn't correspond to the variable names in the code):

      1.  count the month,

      2.  calculate the interest (balance*rate/100) and round to nearest penny,

      3.  add the interest to the balance,

      4.  set the repayment to the amount the user entered

      5.  calculate the minimum repayment according to the percentage rule (balance*percentage/100) and round,

      6.  if the repayment is less than the minimum, set the repayment to the minimum,

      7.  subtract the repayment from the balance and round,

      8.  add the repayment to the total of what's been paid

      9.  if there is still something outstanding (balance>0), go back to step 1, otherwise ...

      10.  add the balance to the total paid (this adjusts the total if the last repayment was more than the balance and the balance is negative).

    The page can then report the number of months the loan took to pay off, the total paid and the total charges by subtracting the opening balance from the total paid.