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16 May

Having contact with the original owner of a slide rule that remembers the year it was purchased helps on determining the age. In general it is safe to assume a linear production rate between the rollover dates particularly for the common types rules.Other Slide Rule dates are currently in development. Please refer to the museum library and individual galleries as this page is being built. Serial numbers can be used to approximate the manufacture date of a given rule however not necessarily the sales date.

Even then, some manufacturers recycled their serial numbers over time, and the stock could have been left on a shelf for a period of time before the slide rule was assembled and shipped. Combined Large 6.47MB Most Keufel & Esser slide rules had serial numbers, but unfortunately they reused their 6-digit serial numbers several times.

To ensure that they stay lustrous, think outside the jewelry box: wearing them regularly will keep them polished, thanks to your body's natural oils.

When you take them off, wipe them with a dry cotton cloth."The best way to clean a diamond is with warm soapy water and a soft-bristle brush or old toothbrush," says Loretta Castoro, vice president and international jewelry buyer for Jewelry Television. You may have heard that using toothpaste gets your diamond to sparkle; it's not a great idea, says Castro.

They did not have the benefit of cheap, off the shelf, mass produced batteries. Bronze is a relatively hard alloy of copper and tin, better suited for the purpose than the much softer copper enabling improved durability of the weapons and the ability to hold a cutting edge.

For many years the telegraph, and later the telephone, industries were the only consumers of batteries in modest volumes and it wasn't until the twentieth century that new applications created the demand that made the battery a commodity item. The use of bronze for tools and weapons gradually spread to the rest of the World until it was eventually superceded by the much harder iron.