https://calcperch.com/guides/ Plain-English guides on photos, money, PDFs, and AI costs from CalcPerch. en-us https://calcperch.com/guides/unix-time-for-beginners/ https://calcperch.com/guides/unix-time-for-beginners/ Fri, 28 Aug 2026 09:00:00 GMT Unix time is just a number of seconds — no dates, no timezones. Why software uses it, why seconds vs. milliseconds breaks things, and what the Year 2038 problem is. https://calcperch.com/guides/watermark-photos-why-how/ https://calcperch.com/guides/watermark-photos-why-how/ Tue, 25 Aug 2026 09:00:00 GMT Watermarks protect some photos and hurt others. When adding one actually helps, when it backfires, and how to place one without ruining the shot. https://calcperch.com/guides/favicon-complete-guide/ https://calcperch.com/guides/favicon-complete-guide/ Fri, 21 Aug 2026 09:00:00 GMT The favicon files browsers, iOS, Android, and Google Search actually check for in 2026, and why favicons silently fail to update. https://calcperch.com/guides/chatgpt-subscription-worth-it/ https://calcperch.com/guides/chatgpt-subscription-worth-it/ Tue, 18 Aug 2026 09:00:00 GMT ChatGPT Plus, Claude Pro, and Gemini Advanced cost about $20/month flat. Who actually comes out ahead paying per token instead, and who shouldn't bother. https://calcperch.com/guides/prompt-caching-explained/ https://calcperch.com/guides/prompt-caching-explained/ Fri, 14 Aug 2026 09:00:00 GMT Prompt caching lets you pay a fraction of the price for tokens you send repeatedly. How OpenAI, Anthropic, and Google implement it, and when it actually saves money. https://calcperch.com/guides/ai-tokens-explained/ https://calcperch.com/guides/ai-tokens-explained/ Tue, 11 Aug 2026 09:00:00 GMT AI models don't charge by the word or the API call — they charge by the token. What a token is, why it's the billing unit, and how to use fewer of them. https://calcperch.com/guides/business-days-vs-calendar-days/ https://calcperch.com/guides/business-days-vs-calendar-days/ Fri, 07 Aug 2026 09:00:00 GMT '5 business days' isn't the same math every time. How weekends, federal holidays, and fine-print definitions change the answer. https://calcperch.com/guides/tip-culture-us-guide/ https://calcperch.com/guides/tip-culture-us-guide/ Tue, 04 Aug 2026 09:00:00 GMT Why American tipping works the way it does, real percentages for restaurants and a dozen other services, and what to do about the tablet screens asking for 30%. https://calcperch.com/guides/bmi-limitations/ https://calcperch.com/guides/bmi-limitations/ Fri, 31 Jul 2026 09:00:00 GMT BMI is a quick screening ratio, not a body-fat measurement. What it misses — muscle, age, ethnicity, fat distribution — and how to read your number sensibly. https://calcperch.com/guides/salary-negotiation-numbers/ https://calcperch.com/guides/salary-negotiation-numbers/ Tue, 28 Jul 2026 09:00:00 GMT A raise percentage, a total comp figure, and an hourly rate mean less than they look like. Here's how to run the actual numbers. https://calcperch.com/guides/rule-of-72-and-savings/ https://calcperch.com/guides/rule-of-72-and-savings/ Fri, 24 Jul 2026 09:00:00 GMT The Rule of 72 turns any interest rate into a doubling time you can calculate without a calculator, and how accurate it really is. https://calcperch.com/guides/apr-vs-interest-rate/ https://calcperch.com/guides/apr-vs-interest-rate/ Tue, 21 Jul 2026 09:00:00 GMT The interest rate and the APR on a loan are almost never the same number — what APR actually includes and when to ignore it. https://calcperch.com/guides/mortgage-payment-explained/ https://calcperch.com/guides/mortgage-payment-explained/ Fri, 17 Jul 2026 09:00:00 GMT Principal, interest, taxes, insurance and PMI — what each piece is, why early payments are mostly interest, and how rate changes the total. https://calcperch.com/guides/url-shortener-guide/ https://calcperch.com/guides/url-shortener-guide/ Tue, 14 Jul 2026 09:00:00 GMT When a short link actually helps, when it just adds risk, and what happens if the shortening service ever shuts down. https://calcperch.com/guides/qr-codes-explained/ https://calcperch.com/guides/qr-codes-explained/ Fri, 10 Jul 2026 09:00:00 GMT How QR codes store data, what they can hold besides URLs, the quishing scam pattern, and how to generate one that scans reliably. https://calcperch.com/guides/password-security-basics/ https://calcperch.com/guides/password-security-basics/ Tue, 07 Jul 2026 09:00:00 GMT What really makes a password strong in 2026, the habits that matter more, and how to generate and store passwords you won't have to remember. https://calcperch.com/guides/how-to-make-transparent-background/ https://calcperch.com/guides/how-to-make-transparent-background/ Fri, 03 Jul 2026 09:00:00 GMT The tools that actually work, the mistakes that ruin the result, and how to keep clean edges on a transparent PNG. https://calcperch.com/guides/jpg-vs-png-vs-webp/ https://calcperch.com/guides/jpg-vs-png-vs-webp/ Fri, 03 Jul 2026 09:00:00 GMT A practical breakdown of JPG, PNG, and WebP — what each one is good at and how to pick the right one. https://calcperch.com/guides/how-to-merge-pdf-files/ https://calcperch.com/guides/how-to-merge-pdf-files/ Fri, 03 Jul 2026 09:00:00 GMT Combining PDFs comes up more than you'd think — here's when to merge, when to split, and how to do both safely. https://calcperch.com/guides/choose-ai-model-by-cost/ https://calcperch.com/guides/choose-ai-model-by-cost/ Fri, 03 Jul 2026 09:00:00 GMT Price tiers, the 80/20 routing rule, and a worked chatbot bill on three models.