第一行 Ttime =now的值 timetostr时间显示为15:08:50 双浮点数double类型，8字节
小数点部分记录时间 0.6311428009 *24=15.1474272216 取整为15， 0.1474272216*60=8.845633296 取整8为分，
0.845633296*60=50.73799776 取整为50为为秒，0.73799776*1000=737为毫秒。
这是时间的计算方法。
如果复制time，整数部分就为0了。
第三行 tDatetime now的，Datetimetostr时间显示为2016-10-08 15:09:55， 双浮点数double类型，8字节
小数点以后的表示的时间，如上计算。
整数部分，表示的日期。自1899-12-30后的天数。
Tdate就是去掉小数部分的内容
网友:1：double数据类型是计算机四种基本类型之一，另外三个是：int，char，float 基本在每一种编程语言当中都有的实现。 2：在delphi当中double也是64位的。 3：c＋＋当中double也是64位， 4：两种编程语言的double范围都是一样的
In Delphi, TDateTime is a type that maps to a Double. In C++, the TDateTime class corresponds to the Delphi TDateTime type.
The integral part of a Delphi TDateTime value is the number of days that have passed since 12/30/1899. The fractional part of the TDateTime value is fraction of a 24 hour day that has elapsed.
Following are some examples of TDateTime values and their corresponding dates and times:
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0
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12/30/1899 12:00 am
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2.75
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1/1/1900 6:00 pm
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-1.25
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12/29/1899 6:00 am
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35065
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1/1/1996 12:00 am
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To find the fractional number of days between two dates, simply subtract the two values, unless one of the TDateTime values is negative. Similarly, to increment a date and time value by a certain fractional number of days, add the fractional number to the date and time value if the TDateTime value is positive.
When working with negative TDateTime values, computations must handle time portion separately. The fractional part reflects the fraction of a 24-hour day without regard to the sign of the TDateTime value. For example, 6:00 am on 12/29/1899 is –1.25, not –1 + 0.25, which would be –0.75. There are no TDateTime values between –1 and 0.