referring now to the drawings , embodiments of this invention will be described . a drug preparation tray 1 is a top - open shallow vessel and has a suitable size for putting drugs therein and hand - carrying . it may be formed from any material light enough for hand - carrying , such as wood , paper and metal . its shape is not limited to that shown . for example , it may carry a lid or may be partially opened on both sides . a display unit 2 is mounted to one side of the tray . it is detachably mounted to the tray 1 so that different types of display units 2 can be used in combination with different types of trays 1 . as shown in fig1 b , the display unit 2 is detachably mounted to the tray 1 by means of hook - and - loop fasteners 1a . the size and number of such fasteners 1a should be determined according to the size of the display unit 2 . it is also possible to detachably mount the display unit 2 to the tray 1 in other ways . for example , the display unit 2 may be connected to one side of the tray 1 by means of fittings provided on the side of the tray or simply by bolts and nuts . mounted in the display unit 2 are a controller 3 , a power source 4 and an input 5 . a display 6 is provided on the surface . fig2 is a block diagram of the control circuit in the display unit 2 . the controller 3 has a memory 3a and a display driver 3b . the power source 4 has its own battery 4a and is further connected to a solar battery 4b . one of the batteries 4a and 4b may be omitted . the input 5 comprises a signal transmitter / receiver 5a , drug type indicating switches 5s and a keyboard 5c . the display 6 is a liquid crystal display . a signal transmitter / receiver 5a is provided on the other side of the display unit 2 and used to input patients &# 39 ; names or codes . it has an idx in the form of a non - contact type ic card carrying a read / write ic memory . in response to light signals transmitted from a light transmitter / receiver fixed in a suitable position in the pharmacy , necessary data are written into or read out of the ic card . the idx may be replaced by a unit that utilizes electric wave or ultrasonic signals . the input 5a may be replaced by the keyboard 5c , or both the input 5a and the keyboard 5c may be provided . such keyboards are used to input drug - related data if manual input is more convenient than inputting such data from the computer or if the computer should break down . one of the drug type indicating switches 5b is closed every time one kind of drug for one patient has been put in the tray to indicate this fact on the display . the liquid crystal display 6a of the embodiment can indicate the instruction data in prescriptions , one line at a time . and instead , a display which can display the entire instruction data in one prescription at a time may be used . conventionally , the letters or codes in each line that represent each drug should be indicated in a different color from the other lines so that viewers can easily distinguish the differences in drugs . the tray of this embodiment is used in the following manner . as mentioned earlier , display units 2 can be detachably mounted to trays 1 . thus , if one display unit 2 mounted to one tray 1 should malfunction , it is possible to replace this display unit 2 with another display unit 2 . prescribed drugs are roughly classified into tablets , powdered drugs , liquid drugs , and external application drugs . in each of the trays are put some or all of the above four types for each patient . each time the drug prescribed for each patient is put in one tray , a correct one of the switches 5b corresponding to the drug is pressed . drugs are prepared in a variety of ways . some pharmacies may have a facility which can prepare and pack drugs fully automatically . other pharmacies having no such facility have to prepare and pack drugs fully manually . when the drugs of one type for one patient are put in a tray , the switch corresponding to tablets is pressed . then , the tray is hand - carried to another preparation table . when all the drugs prescribed for one patient are put in the tray and the corresponding drug type indicating switches are closed , this fact is indicated on the display and the tray is carried to the final inspection station . in this embodiment , the display unit 2 is detachably mounted to the tray 1 , but they may be integral with each other . in this case , some of the parts of the display unit 2 may be provided on the tray 1 . fig3 - 7 show the drug preparation tray of the second embodiment . the function of the drug preparation tray shown in fig3 is basically the same as the first embodiment . it only differs in details of functions . thus , only the elements that are different from the first embodiment will be described . the same functional elements are denoted by the same numerals and their description is omitted . the display unit 2 is detachably mounted to the tray 1 as in the first embodiment but in a different manner . namely , as shown in fig3 b , it is detachably mounted on the tray 1 through a frame 1b . the drug preparation tray of this invention is not only hand - carriable but can be transported on a conveyor line . the display unit 6 has a liquid crystal display 6a and six led displays 6b . the liquid crystal display 6a has such a size and function that it can indicate the letters , figures and marks that represent the drug names prescribed for each patient and the patient &# 39 ; s name . the led displays 6b indicate the number of times the corresponding switches 5s are pressed . fig4 shows a block diagram of the control circuit of this embodiment . though not shown in fig3 this circuit has an audio signal generator 7 and its driving units 3c , 3d . the drug preparation tray of this embodiment can not only indicate drug preparation data and the types of drugs put in the tray , but can indicate various other data such as warning data . such data are indicated according to the flow chart shown in fig5 . when the data signals about patients &# 39 ; names and the kinds of prescribed drugs are transferred from an external computer ( not shown ) into the signal transmitter / receiver 5a of the input unit 5 , these prescription data are written in the memory 3a ( step s1 ). in step s2 , these data are indicated on the liquid crystal display 6a . when the data for one patient has been written and indicated on the display , the timer is cleared ( t = 0 ). in step s3 , the timer is set and the elapsed time is counted on a counter . in step s4 , judgement is made as to whether the elapsed time has exceeded a predetermined time t . if no , the program returns to step s3 . if yes , a warning sign , such as shown in fig6 a , is indicated on the display ( step s5 ). this warning sign indicates that the drug preparation period starting from the input of necessary data has exceeded a standard period within which the drug preparation should be completed . it urges the pharmacist to quicken the work . in this case , a buzzer may be sounded simultaneously when indicating the warning sign . during and independently of the time - counting steps , the timer key 5t , reset key 5r or drug type indicating switches 5s may be operated . by operating these keys and switches , the main flow of the program is interrupted . the timer key 5t is used to check the elapsed time . namely , by pressing this key , the time elapsed since the prescription data were transferred and written is indicated on the display in place of the warning sign ( see fig6 b ). the function of the drug type indicating switches 5s will be described . in this embodiment , six drug type indicating switches 5s are used which represent tablets , tablets packed , powdered drugs , powdered drugs packed , liquid drugs and external application drugs , respectively . every time one of the switches 5s is pressed ( step s11 ), the number is counted on the led display 6b by one ( step s12 ) ( see fig3 a ). when the number on the displays 6b coincides with the number of types of the drugs specified in the prescription , a buzzer is sounded to indicate the completion of drug preparation for one patient ( step s13 ). this buzzer should have a different frequency or be sounded at different intervals / pulses from the warning buzzer so that they are distinguishable from each other . by pressing the reset key 5r once ( step s8 ), the data one step before is indicated on the display . by pressing this key a required number of times , the initial data will be indicated on the display ( step s10 ). thus , it is possible to correct any wrong entry of the data in any previous step by use of the key 5r . when all the drugs specified in the prescription have been put in the drug preparation tray 1 , the tray is hand - carried or transported on a conveyor to a predetermined place . after inspecting and packing the drugs thus collected in trays , they are handed to patients at the pharmacy window . in this embodiment , every time the preparation of drugs for one patient is complete , the data drug preparation data , together with the data denating the time taken for drug preparation , are fed back to a host computer ( not shown ) and recorded so that such data can be used as a reference for determining how the drug preparation process should be carried out .