The calculator in question is the ACR/EULAR (American College of Rheumatology/European League Against Rheumatism) Classification Criteria for Systemic Sclerosis (SSc). This scoring system is used in the diagnosis and classification of systemic sclerosis, a chronic autoimmune disease characterized by fibrosis of the skin and internal organs.

The ACR/EULAR criteria are applicable to patients who present with clinical features suggestive of systemic sclerosis, such as Raynaud's phenomenon, skin thickening, and internal organ involvement. The criteria are designed to identify patients with systemic sclerosis for inclusion in clinical studies and trials, and to aid in the diagnosis in clinical practice.

The clinical utility of this calculator lies in its ability to stratify patients based on the likelihood of having systemic sclerosis. It assigns points for various clinical features and autoantibodies associated with the disease, with a higher score indicating a higher probability of systemic sclerosis.

The ACR/EULAR criteria are not applicable to patients who have a scleroderma-like condition that better explains the manifestations (such as nephrogenic sclerosing fibrosis, generalized morphea, eosinophilic fasciitis, scleredema diabeticorum, scleromyxedema, erythromelalgia, porphyria, lichen sclerosis, graft-versus-host disease, diabetic cheiroarthropathy) or when skin thickening spares the fingers.

ACR/EULAR classification criteria for systemic sclerosis

# Criteria
 # Entry criteria
A. Skin thickening involves the fingers (+25)
B. Alternative scleroderma-like disorder diagnoses causing skin thickening (such as nephrogenic sclerosing fibrosis, generalized morphea, eosinophilic fasciitis, scleredema diabeticorum, scleromyxedema, erythromelalgia, porphyria, lichen sclerosis, graft-versus-host disease, diabetic cheiroarthropathy) are not present (+25)
## Skin thickening
C. Skin thickening of the fingers of both hands extending proximal to the metacarpophalangeal joints (+9)
D. Puffy fingers (+2)
E. Sclerodactyly of the fingers distal to the metacarpophalangeal joints but proximal to the proximal interphalangeal joints (+4)
F. None (+0)
## Fingertip lesions
G. Digital tip ulcers (+2)
H. Fingertip pitting scars (+3) 
I. None (+0)
## Telangiectasia
J. Present (+2)
K. Absent (+0)
## Abnormal nailfold capillaries
L. Present (+2)
M. Absent (+0)
## Pulmonary arterial hypertension and/or interstitial lung disease
N. Present (+3)
O. Absent (+0)
## Raynaud's phenomenon
P. Present (+2)
Q. Absent (+0)
## Systemic sclerosis-related autoantibodies (anti-centromere, anti-Scl-70, and/or anti-RNA polymerase III)
R. Present (+3)
S. Absent (+0)

# Conditions
- score >= 59
- true
- score == 0

2013 classification criteria for systemic sclerosis: an American college of rheumatology / European league against rheumatism collaborative initiative.