Time is what prevents everything from happening at once. ~John Archibald Wheeler

Continuing developments to the mechanisms that drove clocks did eventually lead to increasing accuracy in time keeping.
The invention of the mainspring lead to the development portable timepieces. The inventor of the mainspring is unknown but references to 'clocks without weights' and two surviving examples show that spring powered clocks appeared in the 15th century Europe. The mainspring is a flat ribbon of steel wound in a coil and attached to the gears of a clock. When the mainspring is wound up and released, it drives the gears as it unwinds.
These clocks and watches gained or lost time in such unpredictable amounts that no one thought of using them to tell the time they were seen more as ornaments. These portable clocks were the first timepieces that the more wealthy people could own they weren't worn on the body.

The First Spring Driven Clocks only had an hour hand. The face was not covered with glass. 
The movement was made of iron or steel and held together with tapered pins and wedges,
 screws weren't used till after 1550.

Some sources credit Peter Henlein (1480-1542), a German locksmith  and watchmaker working in Nuremberg as the inventor of the watch as he was a well known craftsman of early "clock-watches" (taschenuhr), ornamental timepieces worn as pendants which were the first timepieces to be worn on the body.
Improvements to the design of the escapement and the methods used to drive these portable timepieces were continually being made.
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When Christiaan Huygens made the first attempt at a marine chronometer in 1673 in France, he used a balance wheel and a spiral spring for regulation. A balance spring, or hairspring, is attached to the balance wheel, it controls the speed at which the wheels of the timepiece turn and so the rate of movement of the hands. Huygens spring was an improvement on the straight spring invented by Robert Hooke, unfortunately his clock remained inaccurate at sea.

Drawing of one of his first balance springs, attached to a balance wheel, by Christiaan Huygens.
Published in his letter in the Journal des Sçavants of 25 February 1675.

John Harrison eventually created his accurate marine chronometer H4 based on the design of a large pocket watch (his design was too complicated to be replicated on mass).
Pocket watches continued to evolve, the box-like shaped was replaced by more rounded and slimmer cases.
Thomas Mudge's lever escapement (1754) was a great leap forward and is still used in mechanical watches, in a modified form, today.  

Queen Charlotte's Lever Watch and Pedestal
Probably acquired by George III for Queen Charlotte in 1770
(Backplate signed Tho Mudge / London)

Queen Charlotte's Lever Watch and Pedestal made in 1770, currently part of the Royal Collection, appears to have been the first timepiece to use this important development, the earliest known example of the lever escapement. Also, this was the first pocket watch to have an automatic device for compensating changes in temperature.
Still at this time watches were still being produced in small batches in small workshops and owned by the wealthy.
In the 18th century jewels were used as bearings, diamonds became part of some pocket watches and oil was used to lubricate and smooth the movement of the watch parts.
The 1850's saw the introduction of machine made watches, made in Switzerland and the United States, these were eventually produced at such low prices that by the end of the century ordinary people could afford a watch.
Read this interesting story about President Lincolns Pocket Watch
The beginning of the twentieth century saw the introduction of the wrist watch, still seen as a piece of jewellery just for women, but following its successful use in service during the First World War (1914-18), increasingly among men.
More about the development of wrist watches in a future blog.