Let's see.
I am going back to high school in my memory.

The metric system is a decimal system, rather like our money system.
The basic units are
Measurement of distance, the meter.
The measure of weight the gram,
The measurement of volume the leader.
I think that distilled water with a density of 1 means that a leader of 
water weighs 1 kilogram, but am not sure about that.

Most of the civilized world uses the metric system.  Therefore we in the 
United States have to convert from metric to the old English system, which 
the English do not use any more.  G-D knows how much this nonconformity 
costs us every year.

A meter is just over a yard in length,  I think 39.1 inches.  making a 
centimeter about .391 inches in length.
The system was based on the diameter of the earth at the equator, which is 
10,000 kilometers.  I think that's right.

a Kilogram is about 2.2 pounds.  I have no idea how this compares to weight 
in stone.

28 grams of water equals an ounce.

The system was to calculate temperature in centigrade, with 100 increments 
between the freezing and boiling point of pure water as measured at sea 
level.

So if we were using the metric system, a half wave dipole, would be 20 
meters in length, or 10 meters either side of the center feed point.  Since 
a yard is less than a meter in length, and that difference is multiplied for 
every meter, a formula to convert the length is necessary.
So frequency in mhz, divided in to 468 gives you the total length of a half 
wave dipole.
at 7 mhz, 7 in to 46 is 6 with a remainder of 4.  7 in to 48 is 6 with a 
remainder of 6.
7 in to 60 is 8 with a remainder of 4.
This gives a figure of 66.8 total length, or 33.4 feet per side.  Since 
their are 12 not 10 inches to a foot, this comes out to 33 and 4 tenths of a 
foot, about 33 feet 5 inches.
actually I think it's 33 feet 4.8 inches.  Close enough for government at 
this frequency, but if you were working at 900 mhz frequencies, quite 
critical.
Others who know better can rip this little story to shreds.