http://www.buyartsuppliesonline.org/parallel-straightedge/
construct a perpendicular bisector of a given segment.?
Use only the two parallel edges of a straightedge (without compass)
This is what I thought: using the straightedge, build a square so that one of the vertex is A (A and B are the extreme of the segment)
____
|.......|
|___ |_____________
A ........... .............. ... B
Do the same with B
____ ......... ...... . ____
|.......| ......... ....... | ...... |
|___ |_________ |____|
A ........... .............. ... B
Now, the diagonal from the first square (I mean the one that is like this / ) forms 45o with AB
The diagonal from the other square forms - 45o with AB
Find their intersection, lets call this point M
.......M
........ ^
...... /...
.../ ..........
/_________
Do the same in the below semiplane and find the symmetric point from M, lets call N
Now draw the line MN
Ana
 |
 ALVIN DRAFTING DRAWING MOBILE PARALLEL STRAIGHTEDGE 60 $134.97 Time Remaining: 13h 29m Buy It Now for only: $134.97 |
 Alvin PXB 24x36 PARALLEL STRAIGHTEDGE BOARD Drafting $99.99 Time Remaining: 18h 25m Buy It Now for only: $99.99 |
 ALVIN Parallel Straightedge Board 20x26 Drawing Draft $74.97 Time Remaining: 1d 7h 5m Buy It Now for only: $74.97 |
 DRAFTING DRAWING BOARD W PARALLEL STRAIGHTEDGE 23X31 $115.99 Time Remaining: 1d 10h 15m Buy It Now for only: $115.99 |
 DRAFTING DRAWING BOARD W PARALLEL STRAIGHTEDGE 24X36 $134.99 Time Remaining: 1d 10h 17m Buy It Now for only: $134.99 |
 PXB Parallel Straightedge Board 18 x 24 ALVIN cutting Art Supplies $24.99 Time Remaining: 1d 17h 56m |
 ALVIN PXB26 20X26 STRAIGHTEDGE PORTABLE PARALLEL DRAFTING BOARD NIB $40.00 Time Remaining: 2d 10h 27m Buy It Now for only: $40.00 |
 MARTIN UNIVERSAL DRAFTING BOARD 23 X 31 PARALLEL STRAIGHTEDGE NIB $50.00 Time Remaining: 2d 10h 44m Buy It Now for only: $50.00 |
 ALVIN Parallel Straightedge Board 24x36 Drawing Draft $92.97 Time Remaining: 2d 11h 19m Buy It Now for only: $92.97 |
 Alvin PXB 18x24 PARALLEL STRAIGHTEDGE BOARD Drafting $79.99 Time Remaining: 2d 18h 5m Buy It Now for only: $79.99 |
 PARALLEL STRAIGHTEDGE 42 IN PLASTIC ROLLERS DRAFTING DRAWING ALVIN MAYLINE NU $199.97 Time Remaining: 3d 7h 3m Buy It Now for only: $199.97 |
 Staedtler Drawing Board with Parallel Straightedge 18 x 24 $60.00 Time Remaining: 4d 17h 14m |
 Parallel Straightedge Board for Drawing and Drafting 20 x 26 $65.99 Time Remaining: 5d 9h 54m Buy It Now for only: $99.99 |
 STAEDTLER Parallel Straightedge Drawing Board 18x24 $80.00 Time Remaining: 5d 11h 19m Buy It Now for only: $80.00 |
 PARALLEL STRAIGHTEDGE DRAFTING DRAWING 30 IN ALVIN GUIDE LINE STRAIGHT EDGE NEW $46.97 Time Remaining: 5d 13h 27m Buy It Now for only: $46.97 |
 PARALLEL STRAIGHTEDGE 36 IN PLASTIC ROLLERS ARMOREDGE MAYLINE DRAFTING DRAWING $289.97 Time Remaining: 6d 10h 29m Buy It Now for only: $289.97 |
 Mayline 42 Inch Parallel Ruling Straightedge with ArmoRedge Drafting Drawing New $299.97 Time Remaining: 6d 10h 34m Buy It Now for only: $299.97 |
 PARALLEL STRAIGHTEDGE 36 INCH METAL ROLLERS DRAFTING DRAWING ALVIN MAYLINE $189.97 Time Remaining: 6d 11h 51m Buy It Now for only: $189.97 |
 PARALLEL STRAIGHTEDGE 48 IN METAL ROLLERS DRAFTING DRAWING ALVIN MAYLINE NU $209.97 Time Remaining: 6d 11h 59m Buy It Now for only: $209.97 |
 Mayline 60 Mobile Parallel Ruling Straightedge Metal Rollers Drafting Drawing $279.97 Time Remaining: 6d 12h 4m Buy It Now for only: $279.97 |
 PARALLEL STRAIGHTEDGE 36 INCH DRAFTING DRAWING ALVIN MAYLINE PLASTIC ROLLERS $189.97 Time Remaining: 6d 12h 24m Buy It Now for only: $189.97 |
 Mayline 60 Inch Parallel Ruling Straightedge Plastic Rollers Drafting Drawing $249.97 Time Remaining: 6d 12h 41m Buy It Now for only: $249.97 |
 60 Parallel STRAIGHTEDGE w Durlin Rollers DRAFTING $128.95 Time Remaining: 6d 14h 46m Buy It Now for only: $128.95 |
 NEW PXB PARALLEL STRAIGHT EDGE DRAFTING TABLE 24 X 36 $49.99 Time Remaining: 6d 17h 57m |
 Alvin 1101 30 Parallel Straight Edge 30in $97.30 Time Remaining: 7d 58m Buy It Now for only: $97.30 |
 Alvin 1101 36 Parallel Straight Edge 36in $103.17 Time Remaining: 7d 58m Buy It Now for only: $103.17 |
 Alvin 1102 36 Parallel Straight Edge 36in $54.86 Time Remaining: 7d 59m Buy It Now for only: $54.86 |
 Alvin 1102 42 Parallel Straight Edge 42in $60.43 Time Remaining: 7d 59m Buy It Now for only: $60.43 |
 Alvin 1102 48 Parallel Straight Edge 48in $63.28 Time Remaining: 7d 59m Buy It Now for only: $63.28 |
 DRAFTING DRAWING BOARD w PARALLEL STRAIGHTEDGE 16 X 21 $69.97 Time Remaining: 7d 8h 58m Buy It Now for only: $69.97 |
 DRAFTING DRAWING BOARD w PARALLEL STRAIGHTEDGE 18 X 24 $61.97 Time Remaining: 7d 9h 2m Buy It Now for only: $61.97 |
 DRAFTING DRAWING BOARD w PARALLEL STRAIGHTEDGE 20 X 26 $64.97 Time Remaining: 7d 9h 6m Buy It Now for only: $64.97 |
 DRAFTING DRAWING BOARD w PARALLEL STRAIGHTEDGE 23 X 31 $79.97 Time Remaining: 7d 9h 14m Buy It Now for only: $79.97 |
 DRAFTING DRAWING BOARD w PARALLEL STRAIGHTEDGE 24 X 36 $99.97 Time Remaining: 7d 9h 18m Buy It Now for only: $99.97 |
 PARALLEL STRAIGHTEDGE DRAFTING DRAWING 42 IN ALVIN NEW $54.97 Time Remaining: 7d 9h 49m Buy It Now for only: $54.97 |
 BOARD W PARALLEL STRAIGHTEDGE 31 DRAFTING DRAWING NEW $89.97 Time Remaining: 7d 9h 53m Buy It Now for only: $89.97 |
 PARALLEL STRAIGHT EDGE TILT BOARD 16x21 Factroy 2nds $89.00 Time Remaining: 7d 16h 55m Buy It Now for only: $89.00 |
 DRAFTING DRAWING BOARD W PARALLEL STRAIGHTEDGE 24X36 $49.99 Time Remaining: 7d 18h 27m Buy It Now for only: $49.99 |
 DRAWING DRAFTING BOARD W PARALLEL STRAIGHTEDGE 23X31 $45.99 Time Remaining: 7d 18h 35m Buy It Now for only: $45.99 |
 PARALLEL STRAIGHT EDGE DRAFTING DRAWING 36 INCH ALVIN GUIDE LINE NEW $49.97 Time Remaining: 9d 8h 20m Buy It Now for only: $49.97 |
 PARALLEL STRAIGHT EDGE BORAD 24x36 FACTORY SECOND $33.88 Time Remaining: 9d 9h 11m Buy It Now for only: $33.88 |
 BOARD W PARALLEL STRAIGHTEDGE 24 DRAFTING DRAWING NEW $74.97 Time Remaining: 9d 9h 39m Buy It Now for only: $74.97 |
 ALVIN DRAFTING DRAWING MOBILE PARALLEL STRAIGHTEDGE 36 $104.97 Time Remaining: 9d 10h 7m Buy It Now for only: $104.97 |
 PARALLEL STRAIGHT EDGE TILT BOARD23x31 Factory 2nds $34.99 Time Remaining: 9d 18h 46m Buy It Now for only: $34.99 |
 DRAFTING DRAWING BOARD W PARALLEL STRAIGHTEDGE 18X24 $39.99 Time Remaining: 10d 8h 46m Buy It Now for only: $39.99 |
 DRAFTING DRAWING BOARD W PARALLEL STRAIGHTEDGE 31X42 $109.99 Time Remaining: 10d 8h 49m Buy It Now for only: $109.99 |
 DRAFTING DRAWING BOARD W PARALLEL STRAIGHTEDGE 16X21 $79.99 Time Remaining: 10d 8h 53m Buy It Now for only: $79.99 |
 DRAFTING DRAWING BOARD W PARALLEL STRAIGHTEDGE 18X24 $89.99 Time Remaining: 10d 8h 57m Buy It Now for only: $89.99 |
 DRAFTING DRAWING BOARD W PARALLEL STRAIGHTEDGE 20X26 $99.99 Time Remaining: 10d 8h 59m Buy It Now for only: $99.99 |
 ALVIN DRAFTING DRAWING PARALLEL STRAIGHTEDGE 30 in NEW Paral Liner Mobile $87.97 Time Remaining: 11d 6h 28m Buy It Now for only: $87.97 |
 PARALLEL STRAIGHT EDGE TILT BOARD 20x26 Factroy 2nds $29.87 Time Remaining: 11d 8h 19m Buy It Now for only: $29.87 |
 ALVIN Parallel Straightedge Board 18x24 Drawing Draft $67.97 Time Remaining: 11d 12h 1m Buy It Now for only: $67.97 |
 PARALLEL STRAIGHTEDGE DRAFTING DRAWING 48 IN ALVIN NEW $59.97 Time Remaining: 12d 10h 57m Buy It Now for only: $59.97 |
 Alvin 1101 48 Parallel Straight Edge 48in $115.43 Time Remaining: 14d 12h 48m Buy It Now for only: $115.43 |
 PARALLEL STRAIGHT EDGE TILT BOARD 30x42 Factory 2nds $39.77 Time Remaining: 15d 9h 37m Buy It Now for only: $39.77 |
 PARALLEL STRAIGHT EDGE BORAD 30x42 FACTORY SECOND $34.87 Time Remaining: 15d 9h 57m Buy It Now for only: $34.87 |
 PARALLEL STRAIGHT EDGE BORAD 20X26 FACTORY SECOND $29.99 Time Remaining: 15d 19h 9m Buy It Now for only: $29.99 |
 ALVIN DRAFTING DRAWING MOBILE PARALLEL STRAIGHTEDGE 48 $119.97 Time Remaining: 16d 5h 55m Buy It Now for only: $119.97 |
 DRAWING BOARD WITH PARALLEL STRAIGHTEDGE 30 X 42 DRAFTING DRAWING NEW $114.97 Time Remaining: 16d 13h 52m Buy It Now for only: $114.97 |
 Alvin PXB24 Parallel Straightedge Drafting Board $45.00 Time Remaining: 17d 2h 8m Buy It Now for only: $45.00 |
 36 Parallel STRAIGHTEDGE w Durlin Rollers DRAFTING $87.45 Time Remaining: 17d 13h 57m Buy It Now for only: $87.45 |
 48 Parallel STRAIGHTEDGE w Durlin Rollers DRAFTING $109.45 Time Remaining: 17d 13h 57m Buy It Now for only: $109.45 |
 54 PARALLEL STRAIGHTEDGE w hdware for Drafting Table $68.59 Time Remaining: 17d 13h 57m Buy It Now for only: $68.59 |
 PARALLEL STRAIGHT EDGE BORAD 16x21 FACTORY SECOND $26.99 Time Remaining: 18d 12h 40m Buy It Now for only: $26.99 |
 BOARD W PARALLEL STRAIGHTEDGE 36 DRAFTING DRAWING NEW $97.97 Time Remaining: 20d 14h 48m Buy It Now for only: $97.97 |
 BOARD W PARALLEL STRAIGHTEDGE 26 DRAFTING DRAWING NEW $77.97 Time Remaining: 21d 11h 10m Buy It Now for only: $77.97 |
 BOARD W PARALLEL STRAIGHTEDGE 21 DRAFTING DRAWING NEW $69.97 Time Remaining: 21d 11h 19m Buy It Now for only: $69.97 |
 Alvin PXB36 24X36 Parallel Straightedge Board NIB $99.00 Time Remaining: 22d 10h 20m Buy It Now for only: $99.00 |
 PXB Laminated Parallel Straightedge White Drawing Board 24 in x 36 in New $108.09 Time Remaining: 22d 15h 55m Buy It Now for only: $108.09 |
 PARALLEL STRAIGHT EDGE BORAD 23X31 FACTORY SECOND $31.88 Time Remaining: 24d 11h 17m Buy It Now for only: $31.88 |
 ALVIN STRAIGHTEDGE DRAFTING DRAWING PARALLEL 48 in NEW $107.97 Time Remaining: 25d 11h 16m Buy It Now for only: $107.97 |
 Alvin PXB 30x42 PARALLEL STRAIGHTEDGE BOARD Drafting $103.96 Time Remaining: 25d 20h 50m Buy It Now for only: $103.96 |
 Alvin PXB24 PARALLEL STRAIGHTEDGE BOARD Drafting Draw $79.99 Time Remaining: 25d 20h 50m Buy It Now for only: $79.99 |
 ALVIN DRAFTING DRAWING ART MOBILE PARALLEL STRAIGHTEDGE 42 ALVIN PARAL LINER NEW $112.97 Time Remaining: 27d 7h 47m Buy It Now for only: $112.97 |
 PARALLEL STRAIGHTEDGE 48 INCH PLASTIC ROLLERS DRAFTING DRAWING ALVIN MAYLINE NEW $209.97 Time Remaining: 27d 10h 29m Buy It Now for only: $209.97 |
 PARALLEL STRAIGHTEDGE 42 INCH DRAFTING DRAWING MAYLINE $199.97 Time Remaining: 27d 10h 43m Buy It Now for only: $199.97 |