As the saying goes.
I regularly walk and swim at my local beach and when it’s high tide the sand can be very soft, the surf a bit rough and the ocean pool gets churned up with the waves – so there’s not always a best time for my walk – so I tend to alternate between mornings and afternoons to pick the low tide timeframe. I had been away for a couple of weeks and decided to check tide times on the Weather Channel – it has an interactive button that downloads a variety of data, including sunrise, sunset and tide times for the day as well as lightning, rain radar and a 10 day outlook.
I decided that being 1 ½ hrs from high tide would be OK – so I went down to the beach only to find it much more like high tide – certainly it didn’t seem to be an ebb tide. Oh well, walk on the promenade and then dip into the “washing machine” of a swimming pool to cool down. Same thing the next day – I left a bit later, being Sunday, but still got the high tide. This time I went to the notice board that the surf patrol fill in – and sure enough high tide time was an hour later than the TV.
Well that got me thinking that maybe the TV was still displaying tide times as Eastern Standard – not Eastern Daylight Saving Time. Digital broadcasting has enabled data feeds from all sorts of sources, meteorology for radar, CTV cameras for the main roads, surf pictures from beaches up and down the coast – and of course tide time and sunrise/sunset times.
I naturally expected that times would be adjusted for daylight saving on these sort of data feeds, after all most applications have programs that cater for a daylight saving system around the world, our computers and mobile phones get automatically updated – and have so for many years. These feeds come direct from applications onto the digital display – and clearly without any modification. To prove my point I selected two towns on the border between two states, one that is on daylight saving and the other that didn’t. Sure enough their tide times were the same. What was interesting is that the sunrise/sunset data had been adjusted for daylight saving.
Why the ramble? Because it’s asking the same question and getting different answers – the consequence of having data in disparate data marts with inconsistent business rules but bringing the data together for reports/analysis. The formula to calculate tide times has been around for centuries and clearly the time factor is fixed. Because sunrise/sunset is the critical parameter that changes with daylight saving – its program has been modified.
A simple oversight that causes a lot of grief if the business rules applied to data are not clearly defined.
