Photography is full of so-called ‘Rules’, most of which can be characterised as aide memoires rather than do-or-die rules. Nevertheless they can help to remind us of better options or guide us as to the right settings to adopt. One ‘Rule’ that falls into the latter category is the ‘Sunny 16 Rule’. As the name suggests this is designed to help select appropriate exposure settings on a sunny day – not we see that many in the West of Scotland 
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To cut a short story short the rule states that: -
On a sunny day, with an aperture of f/16, use a shutter speed of 1/ISO
In other words, set the shutter speed to 1/200 with an aperture of 200, You can also extrapolate these settings for more or less sunny days.
