On a circular, analogue dial, it's always more sensible to have smaller units (larger numbers) on the outside (km/h) and larger units (smaller numbers) on the inside (mph) as is done in most British Lorries and coaches, but for some odd reason not in cars..
If you look at this speedometer with dominant km/h and mph (km/h on the outside) you'll realise that it's quite easy to read both values.
However as most British car speedometers are now, with mph on the outside and km/h on the inside, it makes it extremely difficult to read the km/h value, since they are crammed into a very tight space.
However, km/h only speedometers are, by far easiest to read because they're nice and 'clean' no clutter or any of that... but they're very uncommon in the UK, since we use the mph as a measure of speed. I believe cars with a km/h only speedometer don't pass their M.O.T...