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Planimeter

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measuring wheel measures the distance PQ (perpendicular to EM). Moving from C to D the arm EM moves through the green parallelogram, with area equal to the area of the rectangle D"DCC". The measuring wheel now moves in the opposite direction, subtracting this reading from the former. The movements along BC and DA are the same but opposite, so they cancel each other with no net effect on the reading of the wheel. The net result is the measuring of the difference of the yellow and green areas, which is the area of ABCD.
25: 184: 160: 888: 172: 196: 148: 136: 278:-axis. For the polar planimeter the "elbow" is connected to an arm with its other endpoint O at a fixed position. Connected to the arm ME is the measuring wheel with its axis of rotation parallel to ME. A movement of the arm ME can be decomposed into a movement perpendicular to ME, causing the wheel to rotate, and a movement parallel to ME, causing the wheel to skid, with no contribution to its reading. 248: 210:
calibrated diameter, with a scale to show fine rotation, and worm gearing for an auxiliary turns counter scale. As the area outline is traced, this wheel rolls on the surface of the drawing. The operator sets the wheel, turns the counter to zero, and then traces the pointer around the perimeter of the shape. When the tracing is complete, the scales at the measuring wheel show the shape's area.
287: 260: 580: 883:{\displaystyle {\begin{aligned}&\oint _{C}(N_{x}\,dx+N_{y}\,dy)=\iint _{S}\left({\frac {\partial N_{y}}{\partial x}}-{\frac {\partial N_{x}}{\partial y}}\right)\,dx\,dy\\={}&\iint _{S}\left({\frac {\partial x}{\partial x}}-{\frac {\partial (b-y)}{\partial y}}\right)\,dx\,dy=\iint _{S}\,dx\,dy=A,\end{aligned}}} 213:
When the planimeter's measuring wheel moves perpendicular to its axis, it rolls, and this movement is recorded. When the measuring wheel moves parallel to its axis, the wheel skids without rolling, so this movement is ignored. That means the planimeter measures the distance that its measuring wheel
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The working of the linear planimeter may be explained by measuring the area of a rectangle ABCD (see image). Moving with the pointer from A to B the arm EM moves through the yellow parallelogram, with area equal to PQ×EM. This area is also equal to the area of the parallelogram A"ABB". The
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The Amsler (polar) type consists of a two-bar linkage. At the end of one link is a pointer, used to trace around the boundary of the shape to be measured. The other end of the linkage pivots freely on a weight that keeps it from moving. Near the junction of the two links is a measuring wheel of
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The polar planimeter is restricted by design to measuring areas within limits determined by its size and geometry. However, the linear type has no restriction in one dimension, because it can roll. Its wheels must not slip, because the movement must be constrained to a straight line.
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The images show the principles of a linear and a polar planimeter. The pointer M at one end of the planimeter follows the contour C of the surface S to be measured. For the linear planimeter the movement of the "elbow" E is restricted to the
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There are several kinds of planimeters, but all operate in a similar way. The precise way in which they are constructed varies, with the main types of mechanical planimeter being polar, linear, and Prytz or "hatchet" planimeters. The Swiss
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built the first modern planimeter in 1854, the concept having been pioneered by Johann Martin Hermann in 1818. Many developments followed Amsler's famous planimeter, including electronic versions.
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travels, projected perpendicularly to the measuring wheel's axis of rotation. The area of the shape is proportional to the number of turns through which the measuring wheel rotates.
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as the rotation is proportional to the distance traveled, which at any point in time is proportional to radius and to change in angle, as in the circumference of a circle (
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The justification for the above derivation lies in noting that the linear planimeter only records movement perpendicular to its measuring arm, or when
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Napier Tercentenary Celebration: Handbook of the Exhibition of Napier Relics and of Books, Instruments, and Devices for facilitating Calculation
1713: 1911: 1116: 400: 1837: 76: 1934: 1929: 195: 1550: 1371:{\displaystyle \int _{t}{\tfrac {1}{2}}(r(t))^{2}\,d(\theta (t))=\int _{t}{\tfrac {1}{2}}(r(t))^{2}\,{\dot {\theta }}(t)\,dt.} 1944: 498: 159: 1383: 1939: 1004:
enclosed by the contour, is proportional to the distance measured by the measuring wheel, with proportionality factor
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meaning that the rate at which area changes with respect to change in angle varies quadratically with the radius.
37: 1703: 47: 41: 33: 247: 1871: 1649: 1110: 990:{\displaystyle {\frac {\partial }{\partial y}}(y-b)={\frac {\partial }{\partial y}}{\sqrt {m^{2}-x^{2}}}=0,} 259: 1499: 135: 58: 1454: 319: 230: 1679: 1876: 1759: 222: 98: 1853: 1199: 118: 1881: 1815: 1739: 1097: 306: 1906: 1894: 1833: 1709: 1699: 1827: 1807: 1767: 1731: 1659: 1890: 286: 1779: 1763: 1644: 226: 1949: 1923: 1858: 115: 1771: 310: 177:
A linear planimeter. Wheels permit measurement of long areas without restriction.
1886: 1626:), and shows that a polar planimeter computes the area integral in terms of the 1639: 1866: 1722:
Gatterdam, R. W. (1981), "The planimeter as an example of Green's theorem",
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For a polar planimeter the total rotation of the wheel is proportional to
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A planimeter (1908) measuring the indicated area by tracing its perimeter
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Hodgson, John L. (1 April 1929), "Integration of flow meter diagrams",
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is non-zero. When this quantity is integrated over the closed curve C,
1180:{\textstyle \int _{\theta }{\tfrac {1}{2}}(r(\theta ))^{2}\,d\theta ,} 1000:
The left hand side of the above equation, which is equal to the area
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The connection with Green's theorem can be understood in terms of
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The operation of a linear planimeter can be justified by applying
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Three planimeters: digital, Prytz's (hatchet) and Amsler's (polar)
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How Round is your Circle?: Where Engineering and Mathematics Meet
478:{\displaystyle {\overrightarrow {EM}}\cdot N=xN_{x}+(y-b)N_{y}=0} 221:
Developments of the planimeter can establish the position of the
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can be recognized as the derivative of the earlier integrand
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This vector field is perpendicular to the measuring arm EM:
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Lowell, L. I. (1954), "Comments on the polar planimeter",
1615:{\textstyle {\tfrac {1}{2}}(r(t))^{2}{\dot {\theta }}(t)} 1113:: in polar coordinates, area is computed by the integral 1555: 1553: 1502: 1457: 1386: 1300: 1228: 1131: 1119: 1216: 1020: 902: 583: 564:{\displaystyle \!\,\|N\|={\sqrt {(b-y)^{2}+x^{2}}}=m} 501: 403: 322: 1444:{\textstyle \int _{t}r(t)\,{\dot {\theta }}(t)\,dt,} 1614: 1539: 1485: 1443: 1370: 1179: 1088: 989: 882: 563: 477: 372: 502: 323: 1907:Photo: Geographers using planimeters (1940–1941) 1708:, Princeton University Press, pp. 138–171, 46:but its sources remain unclear because it lacks 1089:{\displaystyle N\cdot (dx,dy)=N_{x}dx+N_{y}dy} 488:and has a constant size, equal to the length 8: 510: 504: 1592: 1591: 1585: 1554: 1552: 1517: 1516: 1515: 1501: 1464: 1456: 1431: 1411: 1410: 1409: 1391: 1385: 1358: 1338: 1337: 1336: 1330: 1299: 1293: 1264: 1258: 1227: 1221: 1215: 1210:vary as a function of time, this becomes 1167: 1161: 1130: 1124: 1118: 1074: 1055: 1019: 970: 957: 951: 936: 903: 901: 860: 853: 847: 833: 826: 789: 766: 755: 745: 731: 724: 702: 692: 672: 662: 651: 634: 628: 614: 608: 595: 584: 582: 547: 534: 516: 503: 500: 463: 435: 404: 402: 324: 321: 77:Learn how and when to remove this message 1700:"Chapter 8: In pursuit of coat-hangers" 1671: 243: 201:Prytz planimeter with wheel at the left 131: 105:of an arbitrary two-dimensional shape. 1540:{\textstyle r(t)\,{\dot {\theta }}(t)} 1698:Bryant, John; Sangwin, Chris (2007), 7: 1486:{\textstyle \int r\,d\theta =2\pi r} 1187:where the form being integrated is 1008:, the length of the measuring arm. 373:{\displaystyle \!\,N(x,y)=(b-y,x),} 1914:Green's Theorem and the Planimeter 942: 938: 909: 905: 812: 792: 777: 769: 710: 695: 680: 665: 291:Principle of the linear planimeter 14: 1832:, New York: Keuffel & Esser, 1800:The American Mathematical Monthly 1791:Modern Geometry with Applications 1752:Journal of Scientific Instruments 1724:The American Mathematical Monthly 1202:in polar coordinates, where both 1784:, The Royal Society of Edinburgh 1111:integration in polar coordinates 258: 246: 194: 182: 170: 158: 146: 134: 23: 1896:As the Planimeter’s Wheel Turns 1859:P. Kunkel: Whistleralley site, 1882:Computer model of a planimeter 1877:Robert Foote's planimeter page 1609: 1603: 1582: 1578: 1572: 1566: 1534: 1528: 1512: 1506: 1428: 1422: 1406: 1400: 1355: 1349: 1327: 1323: 1317: 1311: 1283: 1280: 1274: 1268: 1255: 1251: 1245: 1239: 1158: 1154: 1148: 1142: 1045: 1027: 930: 918: 807: 795: 641: 601: 531: 518: 456: 444: 364: 346: 340: 328: 1: 391:-coordinate of the elbow E. 238:Various types of planimeters 126:Various types of planimeters 309:onto the components of the 1966: 1867:Larry's Planimeter Platter 1872:Wuerzburg Planimeter Page 1778:Horsburgh, E. M. (1914), 1772:10.1088/0950-7671/6/4/302 1912:O. Knill and D. Winter: 1902:Make a simple planimeter 1826:Wheatley, J. Y. (1908), 32:This article includes a 1935:Technical drawing tools 1930:Dimensional instruments 1891:planimeter explanations 1650:Mathematical instrument 301:Mathematical derivation 165:Amsler polar planimeter 61:more precise citations. 16:Tool for measuring area 1616: 1541: 1487: 1445: 1372: 1181: 1090: 991: 884: 565: 492:of the measuring arm: 479: 374: 293: 101:used to determine the 1945:Measuring instruments 1789:Jennings, G. (1985), 1617: 1542: 1488: 1446: 1373: 1182: 1091: 992: 885: 566: 480: 375: 289: 231:second moment of area 1829:The polar planimeter 1551: 1500: 1496:This last integrand 1455: 1384: 1214: 1117: 1100:and the area follow. 1018: 900: 581: 499: 401: 320: 223:first moment of area 99:measuring instrument 1764:1929JScI....6..116H 1200:parametric equation 119:Jakob Amsler-Laffon 1940:Mathematical tools 1854:Hatchet Planimeter 1612: 1564: 1537: 1483: 1441: 1368: 1309: 1237: 1177: 1140: 1086: 987: 880: 878: 561: 475: 370: 294: 93:, also known as a 34:list of references 1715:978-0-691-13118-4 1622:(with respect to 1600: 1563: 1525: 1419: 1346: 1308: 1236: 1139: 1105:Polar coordinates 976: 949: 916: 819: 784: 717: 687: 553: 417: 253:Linear planimeter 87: 86: 79: 1957: 1842: 1822: 1794: 1785: 1774: 1746: 1718: 1684: 1683: 1676: 1660:Shoelace formula 1621: 1619: 1618: 1613: 1602: 1601: 1593: 1590: 1589: 1565: 1556: 1546: 1544: 1543: 1538: 1527: 1526: 1518: 1492: 1490: 1489: 1484: 1450: 1448: 1447: 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1689: 1686: 1685: 1670: 1669: 1667: 1664: 1663: 1662: 1657: 1652: 1647: 1645:Dot planimeter 1642: 1635: 1632: 1611: 1608: 1605: 1599: 1596: 1588: 1584: 1580: 1577: 1574: 1571: 1568: 1562: 1559: 1536: 1533: 1530: 1524: 1521: 1514: 1511: 1508: 1505: 1482: 1479: 1476: 1473: 1470: 1467: 1463: 1460: 1440: 1437: 1434: 1430: 1427: 1424: 1418: 1415: 1408: 1405: 1402: 1399: 1394: 1390: 1367: 1364: 1361: 1357: 1354: 1351: 1345: 1342: 1333: 1329: 1325: 1322: 1319: 1316: 1313: 1307: 1304: 1296: 1292: 1288: 1285: 1282: 1279: 1276: 1273: 1270: 1267: 1261: 1257: 1253: 1250: 1247: 1244: 1241: 1235: 1232: 1224: 1220: 1176: 1173: 1170: 1164: 1160: 1156: 1153: 1150: 1147: 1144: 1138: 1135: 1127: 1123: 1106: 1103: 1102: 1101: 1085: 1082: 1077: 1073: 1069: 1066: 1063: 1058: 1054: 1050: 1047: 1044: 1041: 1038: 1035: 1032: 1029: 1026: 1023: 998: 997: 986: 983: 980: 973: 969: 965: 960: 956: 947: 944: 940: 935: 932: 929: 926: 923: 920: 914: 911: 907: 891: 890: 875: 872: 869: 866: 863: 859: 856: 850: 846: 842: 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1198:For a 574:Then: 383:where 1816:JSTOR 1740:JSTOR 40:, or 1950:Area 1893:and 1834:ISBN 1710:ISBN 1206:and 103:area 1889:'s 1808:doi 1768:doi 1732:doi 1493:). 1191:in 1926:: 1814:, 1804:61 1802:, 1766:, 1754:, 1738:, 1728:88 1726:, 1702:, 1193:r, 233:. 89:A 44:, 36:, 1810:: 1770:: 1762:: 1756:6 1734:: 1682:. 1624:r 1610:) 1607:t 1604:( 1587:2 1583:) 1579:) 1576:t 1573:( 1570:r 1567:( 1561:2 1558:1 1535:) 1532:t 1529:( 1513:) 1510:t 1507:( 1504:r 1481:r 1475:2 1472:= 1466:d 1462:r 1439:, 1436:t 1433:d 1429:) 1426:t 1423:( 1407:) 1404:t 1401:( 1398:r 1393:t 1366:. 1363:t 1360:d 1356:) 1353:t 1350:( 1332:2 1328:) 1324:) 1321:t 1318:( 1315:r 1312:( 1306:2 1303:1 1295:t 1287:= 1284:) 1281:) 1278:t 1275:( 1269:( 1266:d 1260:2 1256:) 1252:) 1249:t 1246:( 1243:r 1240:( 1234:2 1231:1 1223:t 1208:θ 1204:r 1175:, 1169:d 1163:2 1159:) 1155:) 1149:( 1146:r 1143:( 1137:2 1134:1 1084:y 1081:d 1076:y 1072:N 1068:+ 1065:x 1062:d 1057:x 1053:N 1049:= 1046:) 1043:y 1040:d 1037:, 1034:x 1031:d 1028:( 1022:N 1006:m 1002:A 985:, 982:0 979:= 972:2 968:x 959:2 955:m 946:y 934:= 931:) 928:b 922:y 919:( 913:y 874:, 871:A 868:= 865:y 862:d 858:x 855:d 849:S 841:= 838:y 835:d 831:x 828:d 823:) 816:y 808:) 805:y 799:b 796:( 781:x 773:x 763:( 757:S 743:= 736:y 733:d 729:x 726:d 721:) 714:y 704:x 700:N 684:x 674:y 670:N 659:( 653:S 645:= 642:) 639:y 636:d 630:y 626:N 622:+ 619:x 616:d 610:x 606:N 602:( 597:C 559:m 556:= 549:2 545:x 541:+ 536:2 532:) 528:y 522:b 519:( 514:= 508:N 490:m 473:0 470:= 465:y 461:N 457:) 454:b 448:y 445:( 442:+ 437:x 433:N 429:x 426:= 423:N 411:M 408:E 389:y 385:b 368:, 365:) 362:x 359:, 356:y 350:b 347:( 344:= 341:) 338:y 335:, 332:x 329:( 326:N 276:y 225:( 80:) 74:( 69:) 65:( 51:.

Index

list of references
related reading
external links
inline citations
improve
introducing
Learn how and when to remove this message
measuring instrument
area
mathematician
Jakob Amsler-Laffon
Polar planimeter
A planimeter (1908) measuring the indicated area by tracing its perimeter
Amsler polar planimeter
A linear planimeter. Wheels permit measurement of long areas without restriction.
Three planimeters: digital, Prytz's (hatchet) and Amsler's (polar)
Prytz planimeter with wheel at the left
first moment of area
center of mass
second moment of area
Linear planimeter
Polar planimeter

Green's theorem
vector field
Green's theorem
integration in polar coordinates
parametric equation
Curvimeter
Dot planimeter

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