Any site contribution will be rewarded with a free XLC Pro subscription as our way of saying thank you. We do ask you to co-ordinate with site administrators by email to prevent repetition of calculations and we also ask you to follow our advisory notes so that we have a consistency of quality and style across the Repository. We have provided some notes to help you to choose a calculation subject. Don't start the calculation until an administrator has approved your contribution and instructed you to proceed. On completion he will issue a free XLC Pro subscription.

The length of the free subscription depends upon the quality of your calculation, generally a calculation meeting the requirements set out below are awarded a 12 month XLC Pro subscription. Some people don’t follow our guidance and simply send us a calculation they have available to apply typically these don't have any XLC content but we usually award  a free 3 month XLC Pro subscription.

You should follow our advisory notes below:
We understand that we cannot be too prescriptive regarding how to set out your calculations and that users often have good reason for not following our advice. Please adopt our recommendations as far as practical.

1. DON'T REPEAT - Search the repository before you propose a calculation we do not want to repeat ourselves.
2. USE XLC TEMPLATE - Use the XLC calculation template this helps to keep a consistent approach to site calculations. It will help you manage the calculations units. The layout is based upon a traditional pro forma calculation sheet. View the video which explains how to set out a calculation using the XLC template.
3. SHOW EQUATIONS - Display cell formulae using the XLC Add-in. It is important to show how something is calculated as well as the result of the calculation. XLC Ed or XLC Pro can be used to present your cell formulae.
4. IDENTIFY ADD-INS - Clearly identify any other Excel Addins that are required.
5. INCLUDE A SKETCH - Always include a sketch. View this video which explains how to make great sketches with Excel.
6. VALIDATE YOUR CALCULATION - You must validate your calculation, say how you know it's correct. Does the calculation reproduce a result in a publication or book? Has the calculation been independently checked by another person?
7. INCLUDE REFERENCES - Reference relevant text books where ever possible. Copyright prevents us from any physical copying of text books but the calculation method can be encoded into Excel worksheets. The text book reference adds credibility to your calculation and directs users to the calculation theory.
   
8. NO PLAGIARISM - Make sure that you own the calculation. We never want to be accused of plagiarism so you must have the right to give us your calculation.
9. UNPROTECTED WORKSHEETS - Keep worksheets and macros unprotected.
10. ADVERTISE YOURSELF - We are happy for users to include links to their own websites and web pages.

Suggested subjects for your calculation

1. Encode a problem from a classical text book. What nuggets of math gold are currently lying on your bookshelf? Encode a classic problem and validate your solution by checking against a solution in the book. You must pay attention to copyright here. The equations and calculation method are in the public domain can be copied without any copyright infringement. You cannot physically copy sketches or extracts from the published book. Sketches are best redrawn using Excel’s drawing tools. Always give a reference to the book. We will add Amazon links so that anyone wanting to have the theory behind the calculation can obtain the book easily.
2. Classical maths problems. Simultaneous equations, quadratic equations, geometrical formulae, matrix formulae are popular with our users but there are some holes we would like to fill. High school and university maths problems are universally applicable to many disciplines. Why not dust down your old school notes?
3. Expand the functionality of an existing calculation. Let’s take an example, some calculations are biased for an American audience using imperial units (ft, lbs and kips) or American section properties. Why not download it and make it work with metric units and/or European sections or vice versa? You could propose an improvement to any existing calculation in the repository. You may want to use the forum link to discuss your proposal with the calculation’s author. Collaboration is always good way to approach a problem. Choosing a popular calculation with many downloads gives a good indication about how interesting ExcelCalcs users will find the expanded calculation.
4. Add a Wikipedia calculation. Link a calculation to a page in wikipedia. This well used resource covers thousands of useful calculation topics.
5. Make an Excel version of a web based calculator. You can find many web based scripts for doing useful calculations. The trouble is they are fixed on a web page whereas an excel calculation is easily copied and integrated into your own calculation. ExcelCalcs users will find these calculations interesting and they are easy to validate by comparison with the web script results. Some good websites are http://hyperphysics.phy-astr.gsu.edu/, http://www.esdep.org/members/master/, http://www.tribology-abc.com/, http://gowelding.com/, http://www.roymech.co.uk/, https://efatigue.com, http://www.engineersedge.com/, http://www.engineeringtoolbox.com/, http://www.efunda.com/ ...
6. Your specialist area. We all develop specialism’s what’s simple to you might be incredibly useful to others outside your specialism. Don’t underestimate your skills.
7. Any subject and any discipline are very welcome. We seem to have a lot of engineering calculations but we’ll be interested in any subject that requires a calculation.