# * Graphics and algorithms, part 3

Raise your hand if you have an analog wristwatch or clock.  I thought so.  Raise your hand if your classroom (or your child’s class) has an analog clock.  The analog clock is a dinosaur, really, but I think it still has a role to play in helping some kids understand time concepts.  (On a side note, it also reflects our use of the number 12 as a basis for other measurements.)

What are the benefits of using an analog clock to teach time?  I think it creates a sense of how to represent what has happened as time passes.  It certainly explains the common use of expressions such as “half past,” “quarter past,” five ’til,” etc.  Those expressions are still a part of our conversations about time and make less sense on a digital clock.  The relationship between a clock and fractional parts also supports kids’ understanding of both concepts, especially if we use a clock to represent segments of time that don’t always start at 12:00.  If we use an analog clock to compare the amount of elapsed time between 10:10 to 10:30 and 10:40 to 11:00, we teach kids to think flexibly about noncontiguous fractional parts.  Many special needs student are confused by what fraction is represented in the following graphic:

Although an analog clock is one visual for representing elapsed time, I believe a number line better represents this concept.  Here’s an example of measuring elapsed time in 10 minute intervals.  Once a student can do this fluently in five minute intervals, they are likely to extrapolate to one minute intervals without the number line. A number line is also a better link to the use of standard algorithms for adding and subtracting time.  Don’t laugh at my “writing,” please!  My handwriting is bad enough with pen or pencil, much less using a mouse!