The Link > Credit Programs Resources

DOS credit calculator programs (c) Brian Stewart, 1983-2004

Additional Resources

This page provides additional resources to be used in conjunction with the DOS credit programs.

These include:

  • a pick'n'mix of further programs not included in the simpler download packages,
  • some add-in programs to go in the link's 'others' folder, and
  • some documents and other odds and ends.

Additional Programs

The files in the .zip files downloaded here should be added to a standard set of files already in the default directory (usually C:\CREDIT):

Multi-calculator The easiest way to describe this is as a sort of 'what-if?' calculator or simple spreadsheet.  Fill in all the things you know, put the cursor on the one thing you don't know, and hit the 'calculate' key.  The .zip file includes a revised LINK.INI file which adds Multical to the standard menu for the 'Simple' programs set.  If you are using that set, replace the LINK.INI file in it with this one.  Don't use this if you are using other sets, they will automatically add the multi-calculator to Schedule's menu if MULITCAL.BBC is present.
Planner This performs many of the same functions as Multical but from a menu rather than a 'spreadsheet' format.  On the other hand it adds some extra functions too.    You would only need this if you are using the 'Plus' or 'Simple' sets of programs, it's already included in the 'Two' set and TRURATE2.BBC will detect it and add it to its menu.  The .zip file includes revised LINK.INI files (called SIMPLE.INI and PLUS.INI) which add Planner to the standard menu for the 'Simple' or 'Plus' programs set.  Replace the LINK.INI file in your set with the appropriate one in the .zip file - remember to rename it LINK.INI.
Builder This adds the Schedule Builder facility to Schedule, which helps you to deal with building schedules for more complicated cases.  You would only need this if you are using the 'Plus' set of programs, it's no use with the 'Simple' set and is already included in the 'Two' set.  Version 2.0 available from 15 May 2002, which removes a minor bug in printing on network and other 're-directed' printers.

Other(s) Programs

The files in the .zip files downloaded here should be placed in an OTHERS sub-directory to the 'default' or 'network' directory (if you're using a standard installation, make a folder called 'OTHERS' inside C:\CREDIT and put them in there).  To access these programs, key F3 in the Credit Programs Link menu and enter the name of the program file (without the .BBC):

Grapher This program will generate CGA, EGA or VGA line graphs from the logged output of other programs - particularly Schedule (for example to show how the balance outstanding falls over the lifetime of a loan) - see the .doc file for details.
Mortgage Payments This program provides some fairly straightforward mortgage payment calculations and some rate conversions - it's quite old, so please ignore all the stuff about 'MIRAS'.
(Note:  the following two programs have been re-instated as at 19 April 2003 after I discovered that one had the wrong .zip file name and I'd forgotten to put the other on the site!)
Annual Flat Rates Two programs for dealing with annual flat rates in this one.  FLATRATE.BBC calculates annual flat rates and FLATPAY.BBC calculates the repayments for a given flat rate.
Rebate Scheduler This performs a similar job to Schedule, but calculates balances using the Rule of 78 rather than actual interest calculations, so it can show how settlement figures alter over the course of a loan - interesting if used with Grapher and compared with the output of Schedule.
(These additional resources were added to the site on 19 April 2003)
The purpose of this program is to provide a facility similar to Schedule but which will deal with cases where interest is added to the balance outstanding at intervals (generally known as `rests') which are less frequent than the repayments.  This type of charging system is sometimes seen in loans made by banks, often in the less main-stream areas of their lending - for example, loans to small businesses, and differs from the more common method of charging (dealt with by Schedule) in that interest does not compound every month but only every rest.
Remain Scheduler The purpose of this program is to provide schedules, similar to those used by some lenders, which simply record the corresponding values of payments due and received, rather than showing a record of accruing interest and outstanding capital.
Tables A recent addition.  This program generates sections of the Consumer Credit Tables (including revised tables for the new Total Charge Regulations) as HTML files (which saves me the grind of having to sort out all the formatting in BASIC).  Click this for a sample table (use your 'Back' button to come back here).

Technical Papers

This section contains links to papers explaining the maths and logic behind the programs (more may be added later).   They are formatted as HTML documents with equations etc in the form of .gif files and placed inside .zip archives.  To use a document, download the zip file and unzip the contents into a folder.  Then double-click on the index.htm file to view the paper in your browser (they have been optimised for the Risc OS Oregano browser, but also look okay in MS-IE 5.5 and Opera 5.12): A Micro-computer/Calculator-Based Solution to the Calculation of APR.  Provides an exhaustive (and pretty exhausting) explanation of applying the Newton-Rapheson and Bisection methods to APR calculations. A Micro-computer/Calculator-Based Solution to the Calculation of Rebates by the 'Rule of 78' Method.  This paper also contains material on calculating rebates by the 'Actuarial' and 'Reducing Balance' methods.

Miscellaneous Resources

A few more bits and bobs:


The listing of a simple BASIC program, taken from the technical paper in above, which shows the algorithm used for APR calculations.  This should run in GWBASIC or QBASIC, and BBC BASIC provided you change the 'INKEY$' command, which appears just once in the listing, to 'INKEY$(0)'.

Instructions on using the listing for APR calculations can be found in


The listing of a simple BASIC program, taken from the technical paper in above, which shows the algorithm used for Rule of 78 rebate calculations.  It also does Pro-rata Rule calculations but this is a bit of a fudge - it goes all through the Rule of 78 calculation and then throws the answer away and substitutes the much simpler Pro-rata result!  It should run in GWBASIC or QBASIC - but this one's not BBC BASIC compatible.

Instructions on using the listing for rebate calculations can be found in and

PSITRU14.TXT The listing of version 1.4 of the TruPlus program for the Series 3 Psion organiser (see below for another version).  It also provides a simple payment planner facility along the lines of the Planner program.  If you have an earlier version, version 1.4 is updated to take account of the changes to the TCC Regulation in April 2000 - ie the APR is rounded rather than truncated.
TRURATE.PIC Your browser will probably open a save dialogue when you click this link. The series 3 program is in the form of an application and can be installed on the S3's main screen with it's own icon - which is in this file.  To use this link, right-click on it and use your browser's 'Save link document as ...', 'Save target as ...', or whatever, option to save it to your PC.  Then make a directory in the root of your S3's Internal drive called 'OPD' and put the file in there.
PSITRU15.TXT The listing of version 1.5 of the TruPlus program for the Series 5mx Psion organiser.  This is v1.4 for the S3 adapted for the newer machine.  Frankly, the changes made to coding dialogues mean it looks slightly slicker on the old S3, which is surprising, but it all seems to work.  NB: I say 'seems to' because all I've done is transfer the code and amend where necessary to get it going.

To use the Psion listings above, transfer the the text to your Psion with MClink, Slink, PsiWin, Psi FS (if you use Risc OS - I recommend this free package) or whatever, and then load it (import it in the 5mx) into the Program App and translate it.  the Series 3 version is an App (see above for the icon) so after translating you can install it on your main screen with the 'Apps/Install Application' (Psion-I) option on the menu.

The Series 5mx version is not an App - I'd only had my 5mx a few days when I converted it and haven't worked our how to make 5mx Apps yet - so, after translation, you can start the program by selection the Psitru15.opo (or whatever you rename it) icon.


This is a little bit of history - a text listing for the Hewlett Packard 41 series of programmable calculators.  The HP-41C was the target machine when I was developing the 'Trurate' algorithm (although it was mostly worked out and tested on an Acorn Atom) and hence this is the first ever version of the program in use 'in the field'.

This may seem fairly useless because they stopped producing the 41 in 1990 but they were remarkably resiliant pieces of kit (the US advertising used to be of the Timex 'takes a licking and keeps on ticking' type - eg featuring a calculator which were found in the ruins of a house-fire and, despite looking decidedly crispy, still worked) so there's probably a lot of them still about.

You can also get a fully functioning HP-41CX for free, emulated on your desktop, which will run the listing if you type it in, and read a lot more about these great little machines at this site:

The instructions for using the listing to do APR calculations are the same as those for TRURATE.BAS and can be found in the technical paper in above.


If you need a button for a link to this site, just right-click 'em and nick 'em ...

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