	tape0001.zip

	dpgntape  00.01

	what's it for?

	you want to record a program that lasts 2:13, but your videocasette
	only records 2 hours at the sp speed.  find the recording times 
	for sp and lp recording speeds (or any 2 speeds) that will ...

	1)  record the entire program
	2)  completely fill out the tape, and
	3)  maximize recording time at the shorter speed, 
	    which gives better quality image and sound.

	the program handles a combination of any two recording speeds,
	including speeds that don't currently exist.

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	is there a help screen?

	see the second line of any screen.  

	hit f1 in any screen that has 'f1-help' on line 2 or 3

	read the error messages, which blink if you hit an illegal key.

	hit enter.  note which field that the cursor is on.  the 

	error message is for that field.
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	note1:  i get better results (maximum sp recording time) by 
	using the first screen's 'optimal' options (options 0 - 2).
	they assume an SP recording time of 2:02 (not 2:00), an 
	LP recoring time of 4:04 (not 4:00), and an SLP recording 
	time of 6:06 (not 6:00.)  experience shows that this is the true
	recording length of a t-120 videocasette.  i've never run out 
	of tape using this method, although i've come very close.

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	how do you calculate the recording times?

	the formula for calculating the shorter speed actual recording time is


			     (lm - pt)
    	equation 1:  	sr = --------- * sm
			     (lm - sm)
	
	where 	sr = shorter speed actual recording time
		lm = longer speed maximum recording time
		pt = program total run time	
		sm = shorter speed maximum recording time 


		"shorter speed" has the shorter maximum recording time.
		the sp speed will only record for 2 hours on a standard
		videocasette, while the lp speed will record for 4 hours.
		therefore, the sp recording speed is shorter than lp.
		lp is shorter than slp.

		"longer speed" has the longer maximum recording time.
		the slp speed will record for 6 hours on a standard
		videocasette, while the lp speed will only record for 
		4 hours.  therefore, the slp recording speed is longer
		than lp.  lp is longer than sp.

	       	"maximum recording time" is the time you could record
 		the entire videocasette at a given speed.  e.g., the
		maximum recording time at the sp speed on a standard
		videocasette is 2 hours.  the maximum recording time 
		at the lp speed on a standard videocasette is 4 hours.
		the maximum recording time at the slp speed on a standard
		videocasette is 6 hours.
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	why should i accept your calculations?

	the formula comes from two simulntaneous equations.
	the first equation is obvious.

	equation 2:  pt = sr + lr

	where	pt = program total run time	
		sr = shorter speed actual recording time
		lr = longer speed actual recording time

	equation 2 just says that you have to record the entire program.

		     sr	  lr
	equation 3:  -- + -- = 1 
		     sm	  lm

	where 	sr = shorter speed actual recording time
		sm = shorter speed maximum recording time 
		lr = longer speed actual recording time
		lm = longer speed maximum recording time

	equation 3 says that you have to use 100% of the 
	tape's recording time.  (the 100% is the 1 on the 
	right side of the equals sign.)  

	sr	lr
	--  and -- represent the fraction of the tape's recording time
	sm      lm 	

	used by the shorter and longer recording speeds.  e.g., if you
	record for 1 hour at the 2-hour (sp) recording speed, you have used
	1 hour	  1
	------  = - of the tape's recording time.  if you record for 2 hours
	2 hours	  2
							  2 hours   2
	at the 4-hour (lp) recording speed, you have used ------- = -
							  4 hours   4

							    1	  2
	of the tape's recording time.  these two fractions (- and -) must 
							    2	  4

	add up to 1, which represents 100% of tape recording time.



	now solve equation 2 for lr:  lr = (pt - sr)

	substitute (pt - sr) for lr in equation 3:

		    sr   (pt - sr)
       equation 4:  -- + --------- = 1
		    sm      lm


	solve equation 4 for sr ...

	(lm*sr + sm*pt - sm*sr)/sm*lm = 1

                   sr*(lm-sm) + sm*pt = sm*lm

  	                   sr*(lm-sm) = sm*lm - sm*pt		

 		           sr*(lm-sm) = sm*(lm-pt)

			                (lm-pt)
      equation 1 again =>  	   sr = ------- * sm
		                        (lm-sm)	



      using the same method but solving for lr you get ...

					(pt-sm)
      equation 5:  		   lr = -------	* lm
					(lm-sm)

      note that everything to the right of the equals sign in equation 1
      and equation 5 is a constant.  this permits the calculation of the
      variable sr or lr with absolute confidence.  but see the "note1" above
      to get best results.		
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