Ruler for making navigational computations

Claim 1

AN EXTENSIBLE TIME-MEASURE RULER ADAPTED TO BE USED FOR ASCERTAINING TRAVEL TIME AT A DESIGNATED SPEED BETWEEN POINTS ON A MAP COMPRISING AN ELONGATED BASE HAVING A BORE EXTENDING LENGTHWISE OF SAID BASE, AN ELONGATED SLIDABLE MEMEBR OPERATIVELY ENGAGED WITHIN SAID BORE FOR MOVEMENT IN A PLANE SUBSTANTIALLY PARALLEL TO THE LONGITUDINAL AXIS OF SAID BASE TO VARY THE LENGTH OF SAID RULER, SAID SLIDABLE MEMBER HAVING AN OUTER END AND AN INNER END, A SCALE ON SAID RULER MARKED IN UNITS OF DISTANCE PER UNIT OF TIME TO INDICATE VARYING UNITS OF DISTANCE PER UNIT OF TIME DEPENDING UPON THE EXTENT TO WHICH SAID SLIDABLE MEMBER IS MOVED OUTWARDLY FROM SAID BASE, AN ELONGATED ELASTIC MEMBER ANCHORED AT ONE END TO THE OUTER END OF SAID SLIDABLE MEMBER AND AT ITS OTHER END TO SAID BASE WHEREBY MOVEMENT OF SAID SLIDABLE MEMBER VARIES THE LENGTH OF SAID LENGTH OF SAID MEMBER IN PROPORTION TO THE VARIABLE LENGTH OF SAID RULER, A SCALE ON SAID ELASTIC MEMBER MARKED IN UNITS OF TIME, AND A LOCKING ROD OF ABOUT THE SAME LENGTH AS SAID SLIDABLE MEMBER, SAID LOCKING ROD HAVING AN ACTUATING END SECURED TO THE OUTER END OF SAID SLIDABLE MEMBER AGAINST MOVEMENT TOWARDS THE INNER END OF SAID SLIDABLE MEMBER, AND SAID LOCKING ROD HAVING A SECURING END EXTENDING WITHIN SAID BORE IN SAID BASE NORMALLY RESILIENTLY CONTACTING SAID BASE TO LOCK SAID SLIDABLE MEMBER FROM MOVEMENT WITH RESPECT TO SAID BASE AGAINST THE TENSION OF SAID ELASTIC MEMBER.