Guide
What is an eidograph?
An eidograph is a mechanical drawing instrument invented in the early 19th century for making enlarged or reduced copies of drawings — an improved pantograph that stayed accurate at high magnifications. Today the same job takes seconds with an online scale calculator.
How an eidograph works
Where a pantograph traces a drawing with a pen-linked frame of four bars, the eidograph uses a system of weighted parallel bars pivoting above the drawing board. A sliding weight — called a fulcrum weight — is moved along a graduated bar to set the reduction or enlargement ratio; a plumb bob keeps the tracing point, pencil, and pivot exactly in line.
Because the arms are balanced rather than dragged, the eidograph keeps its precision even at large enlargements where a pantograph's joints begin to sag. Victorian and Edwardian engineering offices used eidographs to reduce large survey drawings and enlarge detail work — tasks that today take one entry in a scale calculator.
The instrument was sold by major scientific makers throughout the 19th and early 20th centuries, typically in a fitted mahogany case with a set of interchangeable weights. Fine examples still turn up at auctions and antique tool fairs — see our guide to collecting antique drawing instruments.
Eidograph vs pantograph
| Aspect | Eidograph | Pantograph |
|---|---|---|
| Mechanism | Balanced parallel bars with sliding weight | Linked parallelogram of four bars |
| Accuracy at high magnification | Holds precision; weight-balanced arms | Joints sag; drift grows with enlargement |
| Setting the ratio | Move fulcrum weight to a graduated scale | Reposition pivot holes between bars |
| Typical era | Early 1800s → early 1900s | Invented 1603; still sold as plastic draftsman tools |
Modern alternatives
The eidograph solved one problem: redrawing a figure at a different size without distorting it. That is now a solved arithmetic problem. Instead of balancing brass arms, you compute the target dimensions and draw at the new size directly:
- Scale calculator — the one on this site converts any original size to any ratio or percentage, in mm, cm, inches or pixels. It is the direct digital replacement for the eidograph's graduated bar.
- Scale rulers — triangular scale rules marked 1:1, 1:2, 1:5, 1:50 cover the common ratios for hand drafting and plan reading.
- CAD and vector software — every CAD package scales selections by a typed factor, which is simply the calculator's ratio expressed as a number.
- Photocopiers and scanners — enlargement and reduction percentages follow the same arithmetic: 50% is a 1:2 reduction.
What the instruments keep is character: an eidograph on a stand is a sculpture of Victorian engineering. But for actually getting dimensions right, a free calculator beats brass every time.
Frequently asked questions
Who invented the eidograph?
The eidograph appeared in Britain in the early 19th century; maker's records attribute its development to the instrument trade around London, with several patents and improvements through the 1800s. It is generally treated as a refinement of Christoph Scheiner's 1603 pantograph rather than a wholly separate invention.
Is an eidograph the same as a diagraph?
No. A diagraph (such as the Coradi diagraph) is a related drafting instrument that also enlarges and reduces, but it uses a different linkage — rigid pointed arms rather than the eidograph's suspended weighted bars. Both were sold as drawing-office equipment in the same era.
What is an eidograph worth today?
Complete cased eidographs from known makers regularly sell from around one hundred to several hundred dollars depending on condition and completeness — see our collecting guide for what affects the price.
Ready to scale something? Open the free scale calculator →