OVER 2 YOU, 126 (15/04/03)

MINDREADER

My brother recently emailed me details of a website (www.cyberglass.biz/FlashEx/mindreader.html) that claims to be able to ‘read your mind’. Unbelievably it actually seems to work but I can’t for the life of me see how it does it; can anyone put me out of my misery?

Trish Naylor, via email

After reading many, many Can you Helps? I finally can! I'm afraid the answer doesn't involve mindreading. The site shows a seemingly random pattern of symbols each being allocated a number between 0 and 99. You are then asked to pick any two-digit number and then add those two digits together. Then having done that take the answer away from the original number. (So for example if you pick 23 you add together 2 and 3 to make 5. Then take 5 away from 23 to leave you with the number 18.) You then have to concentrate hard on the symbol allocated against your number (e.g. 18) before asking the machine to announce what your symbol is. Strangely enough the web site always gets it right.

All that is happening is a simple number pattern. When you follow the number selection process through you will always end up with a number divisible by 9. The only possible answers therefore are 9, 18, 27, 36, 45, 54, 63, 72, and 81. So all that is required is for all of these numbers to have the same symbol allocated to them and hey presto as if by magic your number is always predicted. A new 'random' pattern of symbols is then generated and it can trick you all over again. Very clever stuff!
Peter Hampton

For an explanation of the mathematics, think of any 2-digit number, say 35. That's 3 times 10, plus 5. Or in general terms x times 10, plus y. For it to be a 2-digit number x has to be anything from 1 to 9 and y has to be anything from 0 to 9. Add the two digits together: 3 + 5 = 8, or in general terms x + y. Subtract that from the number you first thought of: 35 - 8 = 27. Or in general terms 10x + y - (x + y) = 10x + y - x - y = 9x. That means that the answer is 9, or 18, or 27, ... , up to 81 (multiples of 9).
Margery Allcock

If Trish puts the numbers 1 to 99 in cells A1 to A99 in a spreadsheet and the formula: =A1-(TRUNC(A1,-1)/10+MOD(A1,10)) in B1 (and then copies down to B99) she will note that the result of the suggested sum is always a product of 9. Then take a look at the mind reader page and she will note that the symbol against all the products of 9 is the same. It is that symbol that will appear. Another good site like this is: http://trendy.org/magic/interactivemagic.html try in particular the mysterious rabbit tricks.
Paul Lautman, Southsea, Hants

I still can’t work it out but a computer literate acquaintance suspects that it may have something to do with the computer registering small, involuntary mouse movements, or possibly picking up some sort of vibration emitted by the user. There is clearly something clever going on, should we be worried?

H. Davidson, Bristol

SEEING THE TREES

I have to undertake a project, which involves going round a 40-acre site and recording the name, age and position of all of the trees. What I have in mind is some sort of hand held GPS system that permits "waypoint" logging with a reference code and then having recorded all of the trees (about 1500 I think) I then need to "download" or transfer the data to a suitable piece of software which will take the data and permit full display, editing and printing.
Can anyone help fill in the details?
Ric Ackland-Snow, via email

There are a number of major that Mr Ackland-Snow may encounter. Firstly the accuracy of GPS is at best is about 15m for a basic unit, which might have a maximum number of perhaps 500 waypoints. This will mean that a number of "surveys" would have to be done, each with a potential, individual error of + /- 15 metres. This would make the integrity of the surveys at best doubtful and also if the trees were close together, difficult to find specific trees on site with the hand-held. A Differential GPS (D-GPS) add on unit would improve accuracy to about 3 metres. It would also be extremely difficult to plot this amount of data even on a drawing sheet as large as A0.

My suggestion (subject to suitable sight-lines being available) would be to break the area to be surveyed into smaller, re-establishable blocks that could then be individually surveyed with his hand-held. These could then be plotted using software like GPSTrackmaker, a free download from: www.gpstm.com).      

Fraser Jordan

In round figures, if your plot were square, it would have dimensions of approx. 400m (1/4 mile), making the trees spaced on average some 10 metres apart. I'm not sure how critical accuracy is to your application, but "leisure" type GPS receivers will struggle to produce a realistic map as 10 metres is quite a high tolerance for such a device, particularly
in this case because the foliage will degrade the GPS signal significantly (assuming the trees are more than just saplings!).

If you can get a reasonable GPS reading, the easiest software I have found for working graphically with GPS points and maps is Memory-Map (www.memory-map.co.uk). This is generally for smaller scale maps, such as 1:50,000 OS maps, but it should plot the points you require, and allow you to add information to each point. The other alternative, if you cannot get a good signal or require higher accuracy, is to use professional surveying equipment such as Differential GPS, or an optical instrument such as a Total Station (EDM), and CAD software. Whatever method you adopt, I would suggest sequentially numbering the trees, and recording species etc. with a corresponding number on a laptop, so the information can be easily correlated later.
Ian Chappel, Minehead, Somerset

Most hand-held GPS systems have a 'Mark' key, which stores the current position as a waypoint.  Most also only have the capacity to hold 500 waypoints, so Ric Ackland-Snow may have to map his trees in three batches.  There are a variety of programs, which allow you to download information from a GPS to a PC.  I use a Garmin 12 handheld, with a serial cable and a DOS program called Gardown, available from http://www.anali.demon.co.uk/gardown.htm and free for personal use.  Gardown downloads waypoints as a formatted text file, which can be edited as text or opened in Excel, for example.  It's possible to produce a crude map using Excel by downloading the waypoints or track history in Ordnance Survey grid format, and plotting them on an X-Y (scatter) chart.  Tim Lodge, via email 

Garmin make GPS receivers and map software that will fit the bill, however, a word of caution. GPS receivers don't work terribly well under tree cover particularly when in leaf. Some are better than others depending on the type of built in aerial. The consensus of opinion in the discussion forums say the receivers with patch antenna are the worse. With this in mind if the trees are anything like 30 feet of one another you might find the accuracy of their position a bit suspect. What you might try is contacting the British forum via Geocaching at http://www.geocaching.com/ Go to "Discuss Geocaching" and the UK forum is at the bottom of the page. Post your query and maybe someone local to you might be prepared to go out with you for a trial run.

Clyde Martindill

RADIOGRAM REPAIRS

I have an old radiogram, which is about 45 years old and in need of attention. Is there anyone these days available and capable of repairing old valve equipment?

Norman Musson, Corby, Northants

I have recently had my Bush 'gram of similar vintage restored to good working order, but I reckon the cost was about the same as the purchase price in the early sixties! There is a very good chappie trading as The Wireless Works in Bugle, this being near St Austell, Cornwall. He does a good trade with visitors to the Eden Project -- he is between the A30 and Eden, on the main road in the village of Bugle, his 'phone number is 01726 852284.

Colin J Coomber, Coombe, Cornwall

Right up Norman's street (not geographically though) is The Vintage Wireless Company, Sale, South Manchester, (Junction 6 M60). Alan Marchant is an enthusiastic professional, not speedy with old kit needing difficult-to-source parts, but he brings back to life the seemingly impossibly dead.
David Millachip

The back pages of Hi-fi World magazine contain a number of adverts from companies who still supply and maintain valve kit, including the Vintage Wireless Company at 17 Bell Street London, who repair and restore all valve equipment - telephone 020.7258.3448 or go to: www.vintagewirelesslondon.co.uk

Bob Connell

I can recommend a small company in Cambs. viz: East Coast Wireless, 2 Holt Court, Walpole St Peter, Wisbech, telephone (01945 780808), e-mail: coastwire@aol.com. They have assured me that there is no problem in obtaining valves and Graham Gosling has successfully repaired my old Armstrong amplifier.

Bob Sirett

Your correspondent should contact a gentleman known as 'The Gramophone Man', Philip Knighton, Bush House, 17B South St, Wellington, Somerset   Tel 01823 661618
email: gramman@msn.com
Tim Seddon

Radiocraft at www.radiocraft.co.uk are highly recommended. They'll pick up and delivery nationally.
Steve Ostler

CAN YOU HELP?

Can anyone suggest a simple software package for modelling mechanical components and virtual machines for educational purposes?   Something that would allow you to drag, drop, re-size and combine graphical representations of cogs, gears, levers and cams, and then allow you to run the virtual machine would be ideal.   Some years ago I came across a game called "Incredible Machines" that allowed you to do something similar, but maybe something better has been published since?
Ian Lower, via email

I believe there are functions within Microsoft Excel that deal with various mortgage calculations. Can anyone tell me the correct one to use for calculating how much is left outstanding after a certain period?
P. Mylam, via email

I am a big fan of the seventies sitcom The Good Life and whilst I don’t aspire to full self-sufficiency, I wouldn’t mind having a go at generating at least enough electricity to run my PC and a few lights, from renewable or sustainable sources. Aside from covering my roof with solar panels, are there any more practical methods a reasonably competent DIYer could tackle? 

Bill Clements, via email