fig2 is a systematic diagram showing a part of a tape recorder necessary to effect the present invention , which comprises : a key input part 10 for generating a key command signal required to drive a running mode designated by a user ; a microcomputer 20 for generating a servo control signal according to a corresponding mode by the key command signal and calculating the present remaining time of tape and the period of supply reel by receiving those reel pulses generated in response thereto ; a servo 30 for driving a supply reel motor 40 by the servo control signal of the microcomputer 20 ; a display 50 for displaying the tape remaining time data of the microcomputer 20 ; and a reel frequency generating sensor 60 for sensing the reel pulse of the supply reel motor 40 . a method for measuring the remaining time according to the flowchart shown in fig3 a and 3b is stored and implemented as a program by the microcomputer 20 . the method for measuring the remaining time of tape recorder according to the present invention will be described in detail hereinafter . as the actual running speed of tape varies depending on wound amounts of tape even if a reel is given a turn at a uniform speed of reel motor in the high speed running mode of tape recorder , the remaining time must be calculated by physical measurement . thus , the remaining time is calculated by measuring first the period ( t s ) of reel pulse on the part of supply reel and , in the following period after the tape is unwound by one rotation , a difference of δt as shown from the following formula ( 2 ) is uniformly made to the previous period . ## equ1 ## wherein , t so : the first period of the supply reel t s1 : the period of the supply reel after the tape is unwound by one rotation r so : the first radius of the tape on the part of the supply reel r s1 : the radius of the tape on the part of the supply reel after the tape is unwound by one rotation as n reel pulses are generated invariably per one rotation period from the part of supply reel at this instance , the microcomputer 20 counts the sensed reel pulses and renders r t ( remaining time )= r t - t s ; t s = t s - δt , every time one period passes away . when the number of reel pulses does not amount to n at a standstill , a value t s / n is found and ( t s / n ) is subtracted from the remaining time ( r t ) multiplied by the value counted in the meantime . assuming that 8 reel pulses are generated per period by referring to fig1 a and 1b , in a1 , a time t s newly measured is made the present period of the reel , in a2 , r t is reduced as continuing time up to a2 , in a3 , r t =( last r t )- t s and t s =( last t s )- δt are made , in a4 , r t attains to ( r t in a3 )- 4 ×( t s / 8 ) and t s attains to ( t s in a3 )- 4 ×( δt / 8 ) by reason that the period was given only a half turn and , in a playing condition , r t is reduced second by second . in the event of high speed faster than 200 - times speed , time is reduced at once to the extent of t s time , but it is not felt as unusual to the naked eyes as the reduced time is too short . referring to a5 , it is same as a3 . referring to a6 , it is same as a2 too . in the timing of a7 , one period is wound in a reverse direction and so , the remaining time r t ) attains to ( last r t )+ t s , and t s attains to ( last t s )+ δt , which is reverse to a3 . in a8 , r t attains to ( r t in a7 )+ 2 ×( t s / 8 ), and t s attains to ( t s in a7 )+ 2 ×( δt / 8 ). the method for correctly displaying the remaining time of tape according to the present invention even when the tape runs at a high speed or the speed of tape changes in the tape recorder , is executed as described hereunder . here , we assume that 8 pulses are generated in one rotation period of the supply reel . referring to fig3 a , the microcomputer 20 judges first whether the present remaining time is calculated in the ( b1 ) stage or not . when the existing remaining time is not calculated , remaining time must be found by physical formula by calculating the period t s on the part of a first supply reel . in order to measure the correct t s , remaining time must be measured when placed certainly at the normal speed , i . e ., play mode . thus , the microcomputer 20 proceeds to the ( b2 ) stage and judges whether the tape is playing . if the present condition is not playing , the microcomputer 20 terminates measuring of the remaining time . if the present condition is playing , then the microcomputer 20 measures in the ( b3 ) stage every infinitesimal time until 8 reel pulses are generated . based on this t s , the microprocessor 20 calculates the remaining time r t according to physical algorithm and terminates a process of control . in the case where the remaining time calculation is completed in the said ( b1 ) stage , the microcomputer 20 proceeds to the ( b4 ) stage and judges whether the direction to which the tape runs is forward or reverse . thereafter , if forward , the microcomputer 20 checks in the ( b5 ) stage whether the tape is in the forward directional high speed mode . the high speed mode means the mode in which the running speed of tape is not uniformly controlled by the capstan motor but the tape is made to turn round at a high speed by the reel motor . consequently , when the tape is shifted to the normal speed mode driven by the capstan motor or to the stop mode after tape ran in the high speed mode in the ( b5 ) stage , if high speed running has not passed beyond one period until then , the amount advanced that much must be subtracted in terms of time . at this time , 8 reel pulses are generated from the part of the supply reel during one period . every time one reel pulse is generated , the microcomputer increases the counting value n . when the tape is shifted to the normal speed mode , the microcomputer 20 multiplies in the ( b6 ) stage the counting value n accumulated until then by a value ( t s / 8 ) fixed as the time per pulse . then , if it subtracts the multiplied value from the remaining time r t remained until before that time r t , the result thereof attains to the remaining time in relevant condition . the period t s in such a condition also attains to the present period t s when the value n of the counter accumulated is multiplied by ( δt / 8 ) and subtracted from the preceding period t s . thereafter , fig3 b , the microcomputer 20 judges in the ( b7 ) stage whether the time the tape got out of the high speed mode signifies stop of the tape or signifies that the tape is shifted to a normal speed . in the case where the tape is shifted to a normal speed , the microcomputer 20 proceeds to the ( b8 ) stage and increases or decreases the remaining time . in other words , in the event of normal speed mode , the tape uniformly proceeds at v t = 8 . 15 m / s on the basis of playing condition and so the remaining time is reduced every second by the microcomputer 20 . also , in the case of medium speed like threefold and ninefold speed , the tape is made to proceed at 3 × 8 . 15 m / s and at 9 × 8 . 15 m / s by the capstan motor and so , in the case of threefold speed , one second is increased or decreased every 0 . 333 second depending on a running direction of the tape by the microcomputer 20 . in the case of ninefold speed , one second is decreased or increased every 0 . 111 second . however , when the tape is keeping the high speed mode in the ( b5 ) stage , the microcomputer 20 proceeds to the ( b9 ) stage . when the tape runs at a high speed , a running speed of tape is not uniform and so the microcomputer 20 judges whether the pulses counted amounts to 8 in number in order to subtract the time that the present tape takes to unwind one round , namely , t s , from the present remaining time after one period . in case the reel pulses are not made to one period in the ( b9 ) stage at that time , the microcomputer 20 increases in the ( b10 ) stage the counting value one by one when reel pulses are reversed ( become low ) and records in the rising edge that one period is advanced when 8 reel pulses are counted . in case one period is advanced under high speed mode conditions in the ( b9 ) stage , in the ( b11 ) stage the microcomputer 20 deducts the one period time t s from the remaining time r t to attain the present remaining time r t , and δt is deducted from the period t s to attain a new period t s as the period is reduced to the extent of δt because one period is advanced . in case the tape is driven in a reverse direction in the ( b4 ) stage , the microcomputer 20 checks in the ( b12 ) stage whether the tape is in the high speed mode or not . in case the tape is shifted to the normal speed mode or to the stop mode from the high speed mode at this time , the present remaining time r t can be found by multiplying the counting value n counted until then by the value t s / 8 time per pulse , and adding the multiplied value to the remaining time r t until before that time in the ( b13 ) stage . the present rotation period t s can be found by multiplying the counting value n counted up to now by δt / 8 and adding the multiplied value to the preceding rotation period ts . when the remaining time r t and rotation period t s are found in such a manner as described hereinabove , the microcomputer 20 proceeds to the ( b7 ) stage discussed above . however , in case the tape is under the high speed mode in the ( b12 ) stage , the microcomputer 20 checks in the ( b14 ) stage whether the reel pulse made one periodic rotation . in case one periodic rotation was not made , the microcomputer 20 proceeds to the ( b16 ) stage and performs the same operation as the ( b10 ) stage . if the microcomputer 20 is ascertained that the reel pulse has made one periodic rotation in the ( b14 ) stage , the present remaining time r t is calculated in the ( b15 ) stage by adding the corresponding period time t s to the previous remaining time r t , ( r t + t s ), and the period rotation period t s is also increased to the extent of δt , that is , ( t s + δt ), to attain the present rotation period t s , as progress was made to the extent of one period . as described hereinbefore , the method for measuring the remaining time according to the present invention has the advantage of being able to correctly measure the remaining time of tape even when the tape runs in the normal speed mode or in the high speed mode , or speed is changed or the direction of drive is shifted in the tape recorder .