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Practical Electronics Editorial offices Electron Publishing Tel +61 2 9939 3295 (Australia) Email pe<at>pemag.au Web www.electronpublishing.com Address mail to: Electron Publishing (Australia) PO Box 194, Matraville NSW 2036 Australia Advertising enquiries +61 2 9939 3295 pe<at>pemag.au Editor Nicholas Vinen Publisher Nicholas Vinen Digital subscriptions Stewart Kearn Tel 07918 614662 Online Editor Alan Winstanley Web Systems Kris Thain Production Bao Smith Technical staff Tim Blythman, John Clarke Print subscriptions Practical Electronics Subscriptions PO Box 6337 Bournemouth BH1 9EH Tel 01202 087631 United Kingdom Email pesubs<at>selectps.com Technical enquiries We regret that technical enquiries cannot be answered over the telephone. We are unable to offer any advice on the use, purchase, repair or modification of commercial equipment or the incorporation or modification of designs published in the magazine. Questions about articles or projects should be sent to the editor by email: pe<at>pemag.au Projects and circuits All reasonable precautions are taken to ensure that the advice and data given to readers is reliable. We cannot, however, guarantee it and we cannot accept legal responsibility for it. Some projects and circuits published in Practical Electronics employ voltages that can be lethal. Do not build, test, modify or fix any mains-powered equipment unless you fully understand the safety aspects involved and you use an RCD (GFCI) adaptor. Component supplies Silicon Chip Publications may offer kits or other parts for making our projects, but not in all cases. When kits are not available, readers will need to find and source parts themselves. We advise readers to check that all parts are still available before commencing any project in a back-dated issue. Advertisements Although the proprietors and staff of Practical Electronics take reasonable precautions to protect the interests of readers by ensuring as far as practicable that advertisements are bona fide, the magazine and its publishers cannot give any undertakings in respect of statements or claims made by advertisers, whether these advertisements are printed as part of the magazine, or in inserts. The Publishers regret that under no circumstances will the magazine accept liability for non-receipt of goods ordered, or for late delivery, or for faults in manufacture. Transmitters/bugs/telephone equipment We advise readers that certain items of radio transmitting and telephone equipment which may be advertised in our pages cannot be legally used in the UK. Readers should check the law before buying any transmitting or telephone equipment, as a fine, confiscation of equipment and/or imprisonment can result from illegal use or ownership. The laws vary from country to country; readers should check local laws. 2 Volume 54. No. 9 September 2025 ISSN 2632 573X Editorial Why I don’t put a space between numbers and units International standard ISO/IEC 80000 states that “A space should be used to separate a numerical value and its unit symbol. This space is a non-breaking space and ideally a thin space in typesetting.” Reading Practical Electronics, you will have have noticed that we don’t do that; we put units immediately after a number, for example, 12V, 1.3A or 25°C. This is not because we are lazy; it is a deliberate convention. The reason for this is that, when a number has a unit attached, the numbers and units are inextricably linked. The units can only be changed by a mathematical transformation between that number/ unit pair and another number/unit pair. To separate the numerical value any other way is to invite disaster. So, for example, when calculating 12V × 10, the result is 120V, not 120. However, if you perform the calculation 12V ÷ 10V, the result is 1.2 – a unitless number, not 1.2V. In other words, when operating on either the number or the unit, you always operate on both. I don’t think that adding a thin space makes it look any better (you might disagree). But that is not why we don’t do so; it’s because we want to reinforce the idea that the two parts are inseparable. This has real consequences. Too many students (and some professionals) treat units as afterthoughts, rather than integral parts of physical quantities. We believe that presenting values and units as a unified whole helps reinforce the correct mental model: that “12V” is not just a number with a label, but a distinct and meaningful quantity that cannot be casually separated. There’s also a growing awareness in fields like programming, data science and engineering software that quantities with units are fundamentally different types to plain numbers. Software libraries like Pint (Python) or units-aware spreadsheets make this distinction explicit. If you try to add 12V to 5A, you’ll get an error – and rightly so. Keeping the unit visually connected to the number supports this idea of type safety and helps readers avoid conceptual errors. Finally, it’s worth acknowledging that typographic conventions were created in the print era, when spacing was as much about line justification and aesthetics as semantics. Today, we write and read in digital formats where cut-and-paste, machine parsing, and semantic clarity often matter more. A thin space may look elegant in typeset copy, but it makes it far easier for readers to accidentally copy just the number without the unit. Nicholas Vinen, Electron Publishing (Australia)* Publisher & Editor, Practical Electronics Magazine * a division of Silicon Chip Publications Pty Ltd. Practical Electronics | September | 2025