Strobe
Leave empty while both guides on your printed sheet measure 150 mm. How to measure: see below.
How to use
- Print. Choose your mains frequency and paper, download, and print at Actual size (100%). Never use “Fit” or “Shrink”.
- Check the size. With a ruler, measure between the two marks at the top of the sheet (X1 to X2) and the two on the left edge (Y1 to Y2). Both should read 150 mm.
- Correct if needed. If a reading is not 150 mm, type both readings in the X1 to X2 and Y1 to Y2 boxes above and download again. The new sheet is corrected for your printer: print it and measure once more.
- Cut and fit. Cut out the disc along the outer circle. Cut the two red lines, fold on the dashed line, and press the disc over the spindle.
- Read the speed. Under a filament bulb or a neon lamp, play at the speed you want to check and watch its ring. Bars standing still: correct speed. Bars creeping clockwise: too fast. Counter-clockwise: too slow.
Most LED lamps do not flicker, so the bars never stand still. Time the black mark instead: 100 turns take 180 seconds at 33 1/3 RPM and 133.3 seconds at 45 RPM.
At 50 Hz the lamp flickers 100 times a second, and 45 RPM would need 133 1/3 bars, which no ring can have. So at exactly 45 RPM the 133-bar ring creeps counter-clockwise 1 bar every 4 seconds. Standing still means 0.25% fast.
Print size keeps the disc round and the spindle hole snug. It does not change the speed reading.