Blood Pressure Classifier (SBC)
Classifies blood pressure (optimal, normal, pre-hypertension, stages 1/2/3) per Brazilian SBC guidelines.
SBC 2020 classification (adults ≥18 years). Systolic/diastolic in mmHg.
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Blood pressure classification (SBC 2020)
This calculator classifies office blood pressure (BP) for adults ≥18 years based on the Brazilian Society of Cardiology (SBC) — Brazilian Hypertension Guideline 2020. The category is determined by the higher of systolic (SBP) or diastolic (DBP) value, following category = max(class(SBP), class(DBP)). The categories are: optimal <120/80, normal 120–129/80–84, pre-hypertension 130–139/85–89, stage 1 hypertension 140–159/90–99, stage 2 hypertension 160–179/100–109 and stage 3 hypertension ≥180/110.
Diagnosis of systemic arterial hypertension (SAH) requires confirmation across multiple measurements or by ABPM (Ambulatory Blood Pressure Monitoring — MAPA) or home BP monitoring (MRPA). Hypertension affects roughly 24% of Brazilian adults and is a leading risk factor for stroke, infarction and chronic kidney disease.
Applications
Primary care screening, occupational health exams, cardiovascular risk stratification, monitoring of antihypertensive therapy, public health initiatives and personal tracking of measurements taken at home with a validated device.
FAQ
Is a single high reading enough to diagnose hypertension? No. Diagnosis requires elevated readings on at least two different visits, or confirmation via ABPM/home monitoring, except for stage 3 with target-organ damage.
What is the “white-coat effect”? A transient rise in BP triggered by the clinical environment. ABPM and home monitoring (MRPA) help differentiate it from true sustained hypertension.
Does this calculator replace a doctor? No. It is an educational reference. Diagnosis, treatment and follow-up must be performed by a qualified physician.
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Hemispherical Head MAWP
Calculate the maximum allowable working pressure (MAWP) of a pressure-vessel hemispherical head, MAWP = (2·S·E·t) ÷ (r + 0.2·t), from the allowable stress S (MPa), the joint efficiency E, the available thickness t (mm) and the internal radius r (mm). Each pressure-vessel component has its own MAWP — the maximum pressure IT withstands with its available thickness — and the WHOLE vessel's MAWP is the SMALLEST among all its components' MAWPs (shell, heads, nozzles), since the vessel is as strong as its weakest component. This formula gives the hemispherical head's MAWP, the inverse of that head's thickness calculation. The factor 2 in the numerator (versus 1 in the shell) reflects the greater efficiency of the spherical form: for the same thickness, radius and material, the hemispherical head withstands about DOUBLE the cylindrical shell's pressure. So in a well-designed vessel with hemispherical heads, the cylindrical SHELL is usually the component governing the vessel's MAWP (the weakest), and the heads have margin. Comparing the components' MAWPs identifies the weakest link and guides repairs and reinforcements. Recomputing MAWP with the remaining thickness measured at inspection is part of vessel integrity management. Enter the allowable stress, efficiency, thickness and radius.
Clutch Max Pressure (Uniform Wear)
Calculate the maximum contact pressure in a disc clutch or brake by the uniform-wear assumption, p_max = 2·F ÷ (π·d·(D − d)), from the axial force F (N) and the outer D and inner d diameters (m); the result is in kPa. Under UNIFORM WEAR (the steady state, after disc run-in), pressure is NOT constant over the friction annulus: it is INVERSELY proportional to radius (highest at the inner radius, lowest at the outer), because wear — proportional to pressure × velocity — only becomes uniform if pressure falls with radius (since velocity grows with radius). So the MAXIMUM pressure occurs at the INNER radius (at diameter d), and that peak limits the design. The maximum pressure must be below the friction material's allowable (linings, pads, ceramic or sintered metallic materials — each with its limit, typically hundreds of kPa to a few MPa). Exceeding the allowable leads to accelerated wear, overheating and friction loss (fading). This calculation checks whether a clutch/brake, under the planned actuation force, operates within its material's pressure limit — an essential durability and safety check. Enter the axial force and the outer and inner diameters.
Gear Base Diameter
Calculate the base circle diameter of an involute gear, d_b = d·cos(φ), from the pitch diameter d (mm) and the pressure angle φ (degrees). The base circle is the circle from which the INVOLUTE tooth profile is generated — the standard profile of modern gears. The involute is the curve traced by the tip of a string unwinding from a cylinder: that cylinder is exactly the base circle. The entire active tooth profile (the part that actually transmits force) is ABOVE the base circle; below it there is no involute profile. The base diameter is fundamental in gear geometry because it defines the involute profile and, with it, key properties: the LINE OF ACTION (the line tangent to both base circles of the mesh, along which tooth contact travels, always in the same direction — why involute gears transmit uniform motion), the base pitch and the contact ratio. The relation d_b = d·cos(φ) shows that the pressure angle is the angle between the line of action and the tangent to the pitch circles. It is an essential parameter in designing and manufacturing (generating) involute gears. Enter the pitch diameter and the pressure angle.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.