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Period Tools vs Ohmlark

A side-by-side comparison built from both listings. Blank cells mean the company has not given that detail; we never guess.

Period Tools compared with Ohmlark
DetailPeriod Tools logo Period ToolsOhmlark logo Ohmlark
What it doesFree, accurate cycle and period predictor Electronics calculators for makers
StageStartup Not given
Founded2026 Not given
Based inNot given Not given
Pricing modelFreemium Freemium
PricingAll calculators and guides are free. Period Tools Pro (optional): $4.99/month or $19.99/year. Free: $0 forever. Pro Monthly: $4 per month, cancel anytime. Pro Lifetime: $29 one-time payment.
Key features
  • Predicts next 6 periods
  • Calculates ovulation day
  • Identifies fertile window
  • Private on-device tracking
  • Cloud sync for Pro subscribers
  • No signup required
  • Resistor Color Code: read 4, 5 and 6-band resistors or find bands for a value
  • LED Resistor: pick the current-limiting resistor and power rating
  • Voltage Divider: output voltage, loading effect, or solve R2 for target Vout
  • RC Filter: cutoff frequency, time constant and attenuation at any frequency
  • LC Resonance: resonant frequency, characteristic impedance and Q
  • 555 Timer: astable frequency/duty cycle and monostable pulse width
  • Battery Life: runtime from capacity, active/sleep current and duty cycle
  • PCB Trace Width: IPC-2221 trace width for current and temperature rise
  • Electronics Unit Converter: SI prefixes, AWG to mm², mil to mm, dBm to mW, oz copper
What makes it different
  • No data collection or server storage
  • Uses standard medical calculation methods
  • Honest about limitations and accuracy
  • No aggressive marketing tactics
  • Real E-series resistor values, not ideal numbers
  • Engineering notation input and result sharing as links
  • No ads, no tracking, no sign-up for free calculators
  • Whole-device BOM costing and battery-life summary in Pro
  • Works on phone at the bench
Community votes00
DR (Domain Rating by Ahrefs)15 +1 (up) since last check1 +1 (up) since last check
Trust Flow (Majestic)200
Citation Flow (Majestic)90
Referring domains (Majestic)770

5 details filled in for both companies.

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